Introductory notes
------------------
This tutorial continues your basic knowledge about computer jargon.
In the prior section you learned about:
The seven basic computer operations.
What the difference is between hardware and software and what makes up
software.
The names given to computers of different size and what they are used for.
All five basic hardware elements and how they are generally related.
How the computer thinks of time.
The difference between bits and bytes, not to mention kilo-, mega- and
gigabytes.
Zero is a number!
The concept of addressing.
A word is not necessarily something you read in a book.
What makes up the CPU and its registers, and how these are all related.
What's that -- you don't think you learned all that? Best go back through
the first section. Otherwise press on and learn about input/output
and storage...
Secondary Storage
-----------------
Storage is a term that describes how a computer retains data in a form
for later use. For a personal computer, storage is generally in the
form of either a hard or "floppy" disk. These work in a manner similar
to your tape recorder. Your music is recorded in the form of magnetic
impressions on tape. Computer data appears as magnetic bits (1s or 0s)
placed on a flat magnetic surface.
Of the two kinds of disks (floppy or hard) can you guess:
Which holds the most data?............................HARD
Which is very portable?...............................FLOPPY
Which this tutorial was distributed on?...............FLOPPY
----------
Very good. You already know the basics. Let's press on now.
Floppy disk
-----------
¦
¦ Music is recorded on up to four tracks on your cassette
___________ ¦ tape recorder (left and right channels, both sides).
__________¦ ¦
____¦ _____ ¦ Data is written in a similar manner on computer disks,
___________ ¦ except that there are many more tracks and the tracks
___________ ¦ are arranged as concentric circles on a flat surface.
___________ ¦
¦ Tracks are written to and read from by a read/write
Tracks ¦ head that moves across the surface of the disk in
¦ steps. Most disks have either 40 or 80 tracks (steps)
Sectors ¦ which are numbered from 0 through 39 (or 79), the lower
¦ numbers being on the outer surface of the disk.
Single/Double ¦
sided ¦ ------ Tracks are placed onto
¦ _--------_ Read/write head the disk by a formatting
Density ¦ ---------------- Disk surface program provided with
¦ the disk operating
Handling & ¦ 0 39 system.
safeguards ¦ (79)
¦
Floppy disk
-----------
¦
¦ Tracks are subdivided into smaller units called sectors.
___________ ¦ The number of sectors per track differs with the exact
__________¦ ¦ operating system you are using. PC-DOS version 2.0
____¦ _____ ¦ introduced 9 sectors/track. Version 1.1 used 8 sectors
___________ ¦ per track. New versions of DOS put 15 sectors on 1.2MB
___________ ¦ disks & either 9 or 18 sectors on 3.5" disks. In general,
___________ ¦ you should not use an early version of DOS to write to a
¦ disk formatted by later versions of DOS; it may not work.
Tracks ¦
¦ Since each track is divided into the same number of
Sectors ¦ sectors, you can think of them as pie-shaped sections
¦ of the disk. Each sector is labeled by the operating
Single/Double ¦ system's format utility. These electronic labels enable
sided ¦ the DOS to find information on the disk.
¦
Density ¦
¦ It's probable that you will never have to interact
Handling & ¦ directly with the disk at the track/sector level, but
safeguards ¦ if you have to, be very careful...It's really easy to
¦ mess up a disk by changing so much as a single bit.
Floppy disk
-----------
¦
¦ Floppy disks come in two major grades: single and
___________ ¦ double sided. This means what the statement implies:
__________¦ ¦ the single sided disk is only certified by the
____¦ _____ ¦ manufacturer to be good on one side. The double sided
___________ ¦ disk can place information on both sides. This does not
___________ ¦ mean that there is no magnetic surface on the other side
___________ ¦ of a single sided disk, just that the manufacturer does
¦ not guarantee that the surface will reproduce magnetic
Tracks ¦ pulses at their true intensity, resulting in possible
¦ data errors.
Sectors ¦
¦ You should never use a single sided disk in a double
Single/Double ¦ sided drive. It may work for a bit, but you stand the
sided ¦ real risk of eventually losing data.
¦
Density ¦ There is also the temptation to turn a single-sided disk
¦ over to use the second side. Avoid doing this. When you
Handling & ¦ do, the disk spins in the opposite direction and this
safeguards ¦ could result in scratching or other problems that will
¦ cause loss of data.
Floppy disk
-----------
¦
¦ The final factor in the equation to determine amount of
___________ ¦ data on a disk is the density or number of bits per
__________¦ ¦ inch. Single density records at 2,768 bits per inch
____¦ _____ ¦ & double density is 5,876 bpi; newer disks even higher.
___________ ¦
___________ ¦ While the number of bits per inch is the technical
___________ ¦ definition of density, usually a more practical way to
¦ look at the problem is to look at the number of bytes
Tracks ¦ stored in each sector. Early computers used 128 bytes
¦ per sector, some use 256 and the IBM-PC uses 512.
Sectors ¦
¦ Using this information it is possible to calculate the
Single/Double ¦ capacity of IBM disks:
sided ¦
¦ 512 bytes per sector (This assumes a DOS
Density ¦ x 9 sectors per track version 2.0 or later.
¦ x 40 tracks per side High density or 3.5
Handling & ¦ x 2 sides per disk inch may differ.)
safeguards ¦ -------
¦ 368,640 bytes stored per disk
Floppy disk
-----------
¦
¦ Finally, there is the topic of disk safeguards. At the
___________ ¦ top of a disk is a small notch. If this notch is covered
__________¦ ¦ then the drive mechanism will NOT write to the disk,
____¦ _____ ¦ thus protecting it and making it read only.
___________ ¦
___________ ¦ If you want to write information on the disk, make sure
___________ ¦ that the notch is UNcovered.
¦
Tracks ¦ Also, recall that bits are recorded rather close to
¦ each other. When the disk is spinning, the read/write
Sectors ¦ head travels a few thousandths of an inch above the
¦ disk. Any obstruction will cause the head to jump parts
Single/Double ¦ of the data, or, if the obstruction gets caught by the
sided ¦ head, it might even scratch the disk.
¦
Density ¦ What's big enough to do it? Here are some things:
¦ Fingerprints Smoke Hair (doesn't take much!)
Handling & ¦
safeguards ¦ Some other things to keep magnetic materials away from:
¦ TVs Magnets X-rays Cats & Dogs etc.
Other Formats
-------------
The 360K 5.25-inch floppy disk has long been the staple for removable storage
on IBM-architecture equipment. The AT-class (80286) computers introduced a
new high density format: 15 sectors per track, yielding 1.2MB on a 5.25-inch
disk. The magnetic properties of these 1.2MB disks make them unusable in
360K drives, but for a little more money they provide four times the storage.
+---------+ Since its introduction, the Apple Macintosh computer used
¦¦ ¦¦ smaller 3.5-inch disks with hard plastic shells. With the
¦+-------+¦ introduction of the IBM PS/2 computer line, 3.5-inch disks
¦ +-----+ ¦ became a standard for IBM-architecture as well and many new
¦ ¦ ¦ ¦ ¦ computers offer at least one 3.5-inch drive. The basic 3.5
+---------+ inch drive yields 720K per disk with a high density version
packing 1.44MB onto a 3.5-inch disk. New 3.5-inch formats
double that to 2.88MB by increasing density (bits/inch).
Note that to write to a 3.5-inch disk the write protect hole
must be covered, just the opposite of 5.25-inch disks.
There are new floppy disk formats under development. Newer formats will
include optical media or a combination of magnetic and optical to pack 20MB
and much more on 3.5-inch or smaller disks.
Hard disks
----------
Hard disks work much like floppy disks, just more so. Instead of thin mylar
coated materials, the hard disk uses an aluminum (or other rigid material)
platter covered with a magnetic coating. Also, there is more than one disk
in any drive. They are stacked like records with the number determining the
capacity of the disk.
While hard disks have sectors, because there are multiple surfaces the
term track is not used; cylinder is used in its place (one cylinder
consists of the stack of tracks on all disk platter surfaces).
Because the hard disk spins faster and has increased density over the
floppy, environmental controls must be stricter to prevent dust or other
damaging agents from getting on the platters. The hard disk is therefore
only seen in a sealed unit and one technology associated with sealed units
is termed Winchester technology.
Hard disk capacity ranges from a usual minimum of 40 Megabytes up to several
hundred megabytes or more.
Hard disks (cont)
-----------------
Hard disks vary widely in performance. The type of disk, the method data
is recorded on the disk, the nature of the interface between the computer
and the drive, and several other factors all have a bearing on
performance.
Disks with hundreds of megabytes will typically be partitioned by the
operating system into logical drives of smaller sizes. Before DOS 4.0
the largest partition was 32MB. DOS 4.0 and later support much larger
partitions, allowing you to organize your system any way you wish.
Setting up a hard disk (both partitions and subdirectories) is one of
the most important tasks you have when you first get a new microcomputer.
Take the time to do it with a plan in mind.
If you have a hard disk, be prepared to spend some time backing up your
data. Even with a sealed unit, problems develop, and usually just when
they will hurt you the most.
Actually, good backup should be exercised with any disk, hard or floppy.
Monitor
-------
+-------------------+ You will interact with your computer largely through
¦ +-----------+ ¦ _ ¦ its monitor or video display. It works much like a
¦ ¦ +- -+ ¦ ¦ ¦ television, and some computers actually use a TV.
¦ ¦ ___ __¦ ¦ ¦ ¦ Because of its construction, the monitor is often
¦ ¦ - ¦ ¦ _ ¦ known as a cathode ray tube, or CRT for short.
¦ ¦ +-----+ ¦ ¦ _ ¦
¦ +-----------+ ¦ _ ¦ Monitors come in a variety of kinds. Take a try at
+-------------------+ matching below.
-------------------------------------------------------------------------------
D Alphanumeric A. A single dot on the monitor screen. Multiple ones
form characters.
B Graphic B. The ability to display diagrams or pictures built
up of individual dots.
A Pixel C. Usually has very high resolution, but can only
display one color.
C Monochromatic D. A combination of letters and numbers.
Monitor (cont)
--------------
Some of the terms you'll hear about microcomputer video are defined here:
Monochrome: Original IBM-PC video. Character-based with no graphics
capability. A third party enhancement called Hercules
added graphics capability.
CGA: IBM's first attempt at a color graphic standard. CGA is a low
resolution standard, largely good for games.
EGA: IBM's second attempt at a color graphic standard. At 640x350 dot
resolution, EGA displayed graphics acceptably well but the dot
count did not match the 4x3 aspect ratio of a typical monitor so
software still could not draw a circle by plotting equal numbers
of points on the screen.
VGA: An IBM standard released with the PS/2. The 640x480 resolution is
both good for graphics and has a one to one screen aspect ratio so
circles can be drawn as circles.
Advanced resolutions (Super VGA) continue to be developed.
Input devices
-------------
Two input devices will be your primary interface with your computer:
Keyboard & Mouse
The keyboard is addressed in a separate tutorial. See that for special
characteristics of the IBM-PC keys.
----------
+---------+ The mouse is a slightly different animal. The body of
+-¦ --- ¦ this device contains a ball which, when rolled along
----+ ¦ --- ¦ a desk or other flat object transmits position
¦ --- ¦ information to the computer. Buttons on the mouse
+---------+ activate various functions.
Position is obtained by various means. In some versions of the mouse you
have to use a special pad with grid marks so that optical sensors can
derive position information from the grid.
There are other special input devices, usually reserved for specific tasks.
Output devices
--------------
There are many output devices for your computer. Most have very special
uses and will not be discussed here. Two that deserve note are:
Plotters & Printers
----------
+---------------+ A plotter is a device that uses some mechanism to drive
¦ ¦ ¦ pens in defined horizontal/vertical motions in order to
¦ Plot +-+ _¦ ¦ produce combined text and graphics figures. Most are
¦ +--+ ¦ ¦ ¦ driven by software that not only controls pen motion,
¦ ¦ ¦ but also pen color, with different colors available
+---------------+ depending on the model purchased.
Most personal computer plotters come with a flat bed. Other models are
available with a pen that moves back and forth and wheels that drive the
paper back and forth for the second dimension of motion. Finally, some few
plotters move the pen back and forth and roll a drum with paper attached
to obtain the other dimension.
Printers
--------
By far, paper is the single largest output you will have from your computer.
Despite claims for "paperless" offices, it is still rare to not see printers
outputting reams of paper.
Modern printers come in a variety of types, with many capabilities.
One class is described as non-impact because the actual printing element
never touches the paper. In the other class the print element does touch
the paper, sometimes quite hard. What is it named? IMPACT
Good...let's categorize some printers (chr = character):
IMPACT NON-IMPACT
Dot matrix - Chrs made up of dots Ink-jet - Dots of ink make up chrs
Daisy wheel - Single chr impacts Thermal - Wires burn special paper
Line printers - Prints entire line Laser - Full page printer
Non-impact printers
-------------------
Thermal printers used to be popular, but their use of special paper that
was subject to extraneous marking (not to mention cost). The use of thermal
printers has dropped significantly.
Two others are becoming popular: Ink jet and laser
+---- ______ The ink jet printer "shoots" individual dots of ink to
++---+ the paper, calculating the location of each dot in order
¦----¦ to form individual characters or dot graphics. When
+----+ using these, a good paper is necessary to avoid smearing.
The laser printer is noted for producing a page of text at
,---L¦ a time. In this printer a laser scans a photoactive plate
/ ¦ building up an image of the printed page. Like in a copy
_-----A¦ machine, the plate is dusted with toner which sticks to the
\ ¦ exposed areas. Paper is then placed in contact with the
`---S¦ plate, transferring the image to the paper. A final heat
bonding seals the toner to the paper. This all takes just
+ - a few seconds.
Impact printers
---------------
There are two impact printers you will likely see with a personal computer:
Dot matrix & Daisy wheel (or Thimble)
The difference between the two is in the quality of the output. Dot matrix
printers form characters from individual dots whereas a daisy wheel printer
imprints fully-formed characters, much like a typewriter. The dot matrix is
the more versatile of the two but less likely to be acceptable for business
correspondence.
Both printers impact the paper through a ribbon to transfer ink to the
paper by the hitting element. Dot matrix printers use 9 to 24 individual
wires. +-------------------------+
¦ ..... ¦ ¦
+-+ ¦ Wires . ¦ Letters _ _ _ ¦
¦ +- ¦ ¦ form . ¦ formed \ ¦ / ¦
¦ +- ¦ ¦ letters .... or ¦ by \ ¦ / ¦
¦ +- ¦ ¦ . ¦ impact \¦/ ¦
¦ +- ¦ ¦ . ¦ O --- ¦
¦ +- ¦ ¦ ..... ¦ ¦
+-+ ¦ ¦ ¦
Interface
---------
Whatever printer you choose, you will have to connect it to the computer.
This is called an interface. There are two types: one is serial, do you
know the other? PARALLEL.
Their names describe the functions. Recall that there are eight bits to
a byte (character) of data. In a serial interface each bit is sent to
the printer individually. A parallel interface sends all eight bits at
once. Each interface has its quirks. The key is making certain that you
have the correct one. They will not intermix.
+----------+--_----+-------+ +----------+ +-------+
¦+-----+ ¦ ¦--_---+¦ ¦ ¦+-----+ ¦ ¦-_-_+ ¦ ¦
¦¦ ¦ ¦ ¦--_--+¦¦ ¦ ¦¦ ¦ ¦ ¦ _ ¦ ¦
¦¦ ¦ ¦--_--+-¦ +-+ ¦¦ ¦ ¦ _ +-¦ +-+
¦¦ ¦ ¦ ¦--_--¦ ¦ ¦ ¦ ¦¦ ¦ ¦ ¦ _ ¦ ¦ ¦ ¦
¦+-----+ ¦ ¦--_--¦¦¦ ¦¦¦ ¦+-----+ ¦ ¦ _ ¦¦¦ ¦¦¦
¦ ¦--_--¦ --------- ¦ ¦ ¦ _ ¦ --------- ¦
+----------+--_--¦ ¦ +----------+ +_-¦ ¦
/__________/ +-----------+ /__________/ +-----------+
/__________/ Parallel interface /__________/ Serial interface
Computer Communications
-----------------------
Very often two computers need to "talk" with one another. This is often
accomplished by attaching a modem to each computer and connecting them
via the phone system. The serial port of the computer is used for the
modem since data is usually transmitted over the phone system in serial
form (one bit after another).
Modem is short for MOdulator/DEModulator. The device is presently needed
because computers are digital devices and telephones are designed to
handle analog information. Thus, a translator is necessary at each end
of the phone line. At the transmitting end, the modem converts digital
to analog and at the receiving end, the other modem converts the analog
tones back to digital signals the computer can process. Modems operate
at different speeds, using a variety of data compression techniques.
In order to communicate properly the modems at each end of the line
must use the same communications parameters.
As the telephone system converts from analog to digital, communications
between computers will become more routine and intermediate devices like
modems may not be necessary.
Networks
--------
Networks are another way for computers to communicate with one another.
A network is a group of computers connected together using one of a
variety of media (cables, wires, fiber optic cables, or radio waves).
The connecting media carries signals from each computer to the others
on the network using a common communications protocol. Depending on
how the network is configured each computer can have equal importance
on the network, or there can be a central computer that controls the
network.
Networks are handy for sharing information between workstations, for
managing a large database that several computers must have access to,
and for sharing resources between several computers (e.g. an expensive
printer that everyone can send output to over the network).
Big networks are relatively difficult to set up and maintain. If you
plan to establish a network, extensive planning is recommended.
Summary
-------
That's it. By no means has this been a complete education in computer
terminology, but it should be enough to get you started and able to
understand your friendly(?) computer store salesperson. Some points from
this portion of the tutorial:
Disks are divided into sides, tracks and sectors.
Density (bits per inch) also enters into the disk capacity equation.
To record to a 5-1/4 inch disk the write protect notch must be uncovered.
Keep all floppy disks away from just about everything!
The Winchester hard disk technology is a sealed unit.
Monitors have various characteristics, including color and graphics.
A mouse is an input device as well as a rodent.
Plotters are graphic output devices for diagrams and text.
Printers can be divided into impact and non-impact models.
The most common non-impact printers are ink jet and laser.
Dot matrix and daisy wheel are the two most common impact printers.
Serial interfaces send bits one at a time, parallel send eight at a time.
Modems and networks allow computers to communication with one another.
Didn't get that? Better go back through again. There will be a test.
Note
----
This tutorial deals with the enhanced IBM keyboard. If your keyboard
looks something like:
++ +---++---++---++--+
++ +---++---++---++--+
+----------------++--++---+ You should continue with this
¦----------------¦+++¦++++¦ tutorial. Your keyboard is close
¦-+--------------¦+--+++++¦ enough to the IBM enhanced keyboard
¦----------------¦ ++ ++++¦ to have the diagrams in this
¦--+----------+--¦++++++++¦ tutorial conform to your keyboard.
+-++----------++-++--++---+
If your keyboard has a column of function keys on the left side:
+---+ Then you want to exit here (press the ESCape key, then zero
+-+-¦ from the main menu) and restart the TUTOR.COM program with
+-+-¦ the command:
+-+-¦ TUTOR OLDKEY
+-+-¦
+---+ If you have any other keyboard the key functions will be the
same; the location will be different.
+--+ +--------------------------------------++------------+
¦Es¦ ¦f1¦f2¦f3¦f4¦f5¦f6¦f7¦f8¦f9¦f10¦f11¦f12¦¦ P ¦SLk¦P Bk¦
+--+ +--------------------------------------++------------+
+-------------------------------------------++------------++---------------+
¦~`¦1!¦2@¦3#¦4$¦5%¦6^¦7&¦8*¦9(¦0)¦-_¦=+¦ BS¦¦Ins¦Hom¦PgUp¦¦NLk¦ / ¦ * ¦ - ¦
¦-------------------------------------------¦¦---+---+----¦¦---+---+---+---¦
¦Tab¦Q ¦W ¦E ¦R ¦T ¦Y ¦U ¦I ¦O ¦P ¦[{¦]}¦| \¦¦Del¦End¦PgDn¦¦7Hm¦8 ¦9Pu¦ ¦
¦---+--+--+--+--+--+--+--+--+--+--+--+------¦+------------+¦---+---+---¦ + ¦
¦Clk¦A ¦S ¦D ¦F ¦G ¦H ¦J ¦K ¦L ¦;:¦'"¦-+C/R¦ ¦4 ¦ 5 ¦6 ¦ ¦
¦-------------------------------------------¦ +---+ ¦---+---+---+---¦
¦ ¦Z ¦X ¦C ¦V ¦B ¦N ¦M ¦,<¦.>¦/?¦ ¦ ¦ ¦ ¦1En¦2 ¦3Pd¦ ¦
¦--------------------------------+----------¦+---+---+---+ ¦-------+---¦C/R¦
¦Ctrl¦ ¦Alt¦ Space ¦Alt¦ ¦Ctrl¦¦ ¦ ¦ ¦ ¦ 0 Ins ¦.De¦ ¦
+----+ +-----------------------------+ +----++-----------+ +---------------+
The enhanced PC keyboard consists of four sections, broadly described below:
Function keys The group of 12 keys on the top of the keyboard.
Alphanumeric keys The section on the left that works much like a
typewriter.
Cursor control keys The center group of keys that move the cursor.
Numeric keypad The keys on the right that switch function
between number entry and cursor control.
Press any key to continue...
+--+ +--------------------------------------++------------+
¦Es¦ ¦f1¦f2¦f3¦f4¦f5¦f6¦f7¦f8¦f9¦f10¦f11¦f12¦¦ P ¦SLk¦P Bk¦
+--+ +--------------------------------------++------------+
+-------------------------------------------++------------++---------------+
¦~`¦1!¦2@¦3#¦4$¦5%¦6^¦7&¦8*¦9(¦0)¦-_¦=+¦ BS¦¦Ins¦Hom¦PgUp¦¦NLk¦ / ¦ * ¦ - ¦
¦-------------------------------------------¦¦---+---+----¦¦---+---+---+---¦
¦Tab¦Q ¦W ¦E ¦R ¦T ¦Y ¦U ¦I ¦O ¦P ¦[{¦]}¦| \¦¦Del¦End¦PgDn¦¦7Hm¦8 ¦9Pu¦ ¦
¦---+--+--+--+--+--+--+--+--+--+--+--+------¦+------------+¦---+---+---¦ + ¦
¦Clk¦A ¦S ¦D ¦F ¦G ¦H ¦J ¦K ¦L ¦;:¦'"¦-+C/R¦ ¦4 ¦ 5 ¦6 ¦ ¦
¦-------------------------------------------¦ +---+ ¦---+---+---+---¦
¦ ¦Z ¦X ¦C ¦V ¦B ¦N ¦M ¦,<¦.>¦/?¦ ¦ ¦ ¦ ¦1En¦2 ¦3Pd¦ ¦
¦--------------------------------+----------¦+---+---+---+ ¦-------+---¦C/R¦
¦Ctrl¦ ¦Alt¦ Space ¦Alt¦ ¦Ctrl¦¦ ¦ ¦ ¦ ¦ 0 Ins ¦.De¦ ¦
+----+ +-----------------------------+ +----++-----------+ +---------------+
Each of these sections contains keys with special meaning to the PC.
These special keys will be covered in this tutorial. The standard
typewriter keys will not. We assume that you know how to type (or at
least "hunt and peck").
Before we can start with a detailed description of the keyboard, you
need to understand the concept of a buffer, something the keyboard and
other parts of the computer uses.
Buffers
-------
A buffer is a temporary storage area in the computer's memory. It is
necessary because activities that require input or output are generally
much slower than those that only interact with memory. Text from the
keyboard is therefore placed into a buffer until you signal the computer
you are done. The computer will then act on what was entered. The signal
is usually the Carriage Return or Enter key. Buffers vary in length;
the DOS command line buffer, for example, can contain up to 127 characters.
+-------------------+
¦___________________+- T e x t f r o m t h e k e y b o a r d
¦___________________¦
¦___________________¦ T e x t f r o m t h e k e y b o a r d
+-------------------+ +--------------------------------------------- ...
Keyboard Buffer
When text is entered into the keyboard buffer, it usually stays there
until replaced, even if brought into the computer as a command and acted on.
DOS allows limited editing of the buffer using the function keys. That will
be the first subject of the keyboard tutorial.
+--------------------------------------+
¦f1¦f2¦f3¦f4¦f5¦f6¦f7¦f8¦f9¦f10¦f11¦f12¦ Function keys:
+--------------------------------------+
The 12 function keys assume different roles for different programs.
F1 through F5 have special meaning within DOS. They help in reissuing or
editing the last DOS command typed.
Two keys redisplay the line currently in the buffer:
+--+
¦F1¦ Redisplays the buffer, one character at a time,
+--+ each time F1 is pressed.
+--+
¦F3¦ Redisplays the entire buffer.
+--+
For example, if A>TYPE \MYPATH\MYFILE were the last DOS command typed,
then pressing F3 would retype the line completely, and pressing F1
nineteen times would reshow the line, a character at a time.
+--------------------------------------+
¦f1¦f2¦f3¦f4¦f5¦f6¦f7¦f8¦f9¦f10¦f11¦f12¦ Function keys:
+--------------------------------------+
The 12 function keys assume different roles for different programs.
F1 through F5 have special meaning within DOS. They help in reissuing or
editing the last DOS command typed. Two keys help edit the buffer:
+--+
¦F2¦ Redisplays the buffer UP TO the character
+--+ you typed after pressing F2.
+--+
¦F4¦ Deletes all characters in the buffer UP TO
+--+ the character you typed after F4. The buffer is
not displayed. To see the buffer on screen tap F3.
For example: Assume the last line typed was A>TYPE \MYPATH\MYFILE
Pressing F2 F would display A>TYPE \MYPATH\MY
(Helps when you want to add to a prior command.)
Pressing F4 \ F3 would display A>\MYPATH\MYFILE
( F4 \ edits the buffer, F3 displays it. )
+--------------------------------------+
¦f1¦f2¦f3¦f4¦f5¦f6¦f7¦f8¦f9¦f10¦f11¦f12¦ Function keys:
+--------------------------------------+
The 12 function keys assume different roles for different programs.
F1 through F5 have special meaning within DOS. They help in reissuing or
editing the last DOS command typed.
And, then there was one:
+--+
¦F5¦ Stores the current line for further editing.
+--+
This key is used with the other four keys to give you the
ability to easily fix errors in long command strings.
When you press the F5 key your current line will be marked and
the cursor will be moved to the next line, without showing a
new prompt. Use the other function keys to finish editing.
Introduction
------------
History is fascinating. The byplay of people and things forms an
interesting and intricate pattern which we can only briefly look at here.
If the subject interests you, here are two references:
For the development of the personal computer:
Fire in the Valley
by Paul Freiberger & Michael Swaine
(Osborne/McGraw-Hill: Berkeley, 1984)
ISBN 0-88134-121-5
For computers in general:
Bit by Bit
by Stan Augarten
(Ticknor & Fields: New York, 1984)
ISBN 0-89919-302-1
Both of the above are easy to read and have favorable reviews from others.
The Beginning
-------------
Computing by machine started (as near as we now know) in the mid-east with
the use of counting stones in channels. This was the precursor of a
counting instrument invented by the Babylonians and normally associated
with the Chinese. Can you name it? The ABACUS.
The abacus reigned supreme for a great while because to use it you really
didn't have to know anything about the theory of numbers. The uneducated
could be trained to use it easily.
Math with Arabic numbers entered Europe in the 8th and 9th centuries. It
did not catch on because the user had to understand theory. To help,
various mechanical devices were invented. In the early 1600s Napier (the
inventor of logarithms) developed a series of rods that could be used for
multiplication.
Partial products appeared on the rods and all the user had to do was add
them to get the final product.
This led to ever more complicated mechanical devices based on gears and
rods,
with Blaise Pascal's mechanical Pascaline being the most famous.
These all lead us to 1791...
Charles Babbage & the Countess of Lovelace
------------------------------------------
No, it's not a soap opera. Babbage was an English mathematician and
inventor and the Countess of Lovelace was Ada Byron, daughter of Lord
Byron, the famous poet.
What do these two have to do with computers? A great deal...
Babbage is often thought of as being the father of computers because of
his inventions. Ada is usually considered to be the first computer
programmer because of her analyses and explanations of Babbage's work.
What Babbage did to achieve such fame is develop the ideas for two
"engines," or mechanical calculators.
The Difference Engine, a model of which was built, solved polynomial
equations by the method of differences.
The Analytical Engine, never built, was designed to be a general purpose
computing device.
Neither machine was produced because tooling of the day was not good
enough.
Babbage's Contribution
----------------------
While neither of his machines were built in their final form, Babbage
nevertheless left detailed designs that contained within them the heart
of modern-day computers.
The Analytical Engine, in particular, was designed with five parts common
to today's computers:
- An input device Borrowing an idea from textile mills,
a form of punched cards were the input.
- A processor (calculator) A mill containing hundreds of vertical
axles and thousands of gears, 10 feet tall.
- The control unit A barrel-like device with slats and studs,
operating like a complex player piano.
- Storage The store, containing more axles and gears.
This device could hold 100 40-digit numbers.
- An output device Plates designed to fit in a printing press.
Herman Hollerith and the 1890 Census
------------------------------------
The 1880 census of the United States took some 7 or more years to complete
because all processing was done by hand from journal sheets. Because the
population was growing rapidly, hand tabulation in 1890 would likely take
longer than the 10 year period to the next census. A competition was held
for a better method and Herman Hollerith, a Census Department employee,
came up with his "better mousetrap." It would have been used by Babbage
and came from the textile industry.
Can you guess what? PUNCHED CARD Yep, the "do not fold, spindle or
mutilate" card made its entry into the world of numbers here. With it
the initial results of the 1890 census were able to be announced within
six weeks (62,622,250 in case you were interested).
Using the cards, the Census Department was able to produce many different
statistics for the nation - so many that despite the speed and use of the
information, the cost went up to about double the 1880 census; a vision
of times to come where instant information demands processing, whether
useful or not.
Hollerith went on to found the Tabulating Machine Company; to become IBM.
W O R L D W A R II
--------------------
As usual, the war effort was a spur to advanced development of technology.
Computers were no exception -- in fact, this is the era where the first
true electronic digital computers were introduced.
T ¦ Mark I ¦ An electromechanical device, using relays, built for the
h ¦ ¦ Navy by IBM. Last of its breed. Overtaken by electronics.
e ¦ ¦
¦ Colossus ¦ Special purpose code breaker built for the British. Used
m ¦ ¦ on German radio codes.
o ¦ ¦
s ¦ ABC ¦ For Atanasoff-Berry Computer, built at Iowa State. Now
t ¦ ¦ known as the first electronic digital computer.
¦ ¦
f ¦ ENIAC ¦ Most famous of the early computers, containing 18,000
a ¦ ¦ vacuum tubes. Built for the Army for ballistics.
m ¦ ¦
o ¦ Manchester¦ Built by Manchester University; the first "stored
u ¦ Mark I ¦ program" computer. Up to this time, all computers had
s ¦ ¦ be be told what to do by rewiring. This was a
breakthrough.
The Generations
---------------
The move from World War II to the present can be divided into roughly four
generations -
/ Running from roughly 1951 through 1958, generation one
First -< computers are characterized by their use of vacuum tubes.
\
\ The standout of the era is the UNIVAC (UNIVersal Automatic
\ Computer) which was the first true general purpose computer
Second \ in America designed for both alphabetic as well as
\ numeric uses. This made the UNIVAC a standard for
\ business, not just science and the military.
\
Third \ Punched cards formed the input to the machines and
\ all programming was done in machine language (i.e.
\ numbers that were interpreted by the machine as
\ commands.
Fourth \
The Generations
---------------
The move from World War II to the present can be divided into roughly four
generations -
First - 1951 to 1958 - Vacuum tubes - UNIVAC computer.
/ The transistor dominated computers during the period
/ 1959 to 1964. Computers became smaller.
Second -<
\ There were no outstanding computers during this period,
\ however it was famous for development of higher order
\ languages. Computers could now be programmed with
Third \ English-like commands instead of strings of numbers.
\ Programming efficiency improved greatly.
\
\ FORTRAN for scientists and COBOL for business were
Fourth \ the two major languages of the era.
The Generations
---------------
The move from World War II to the present can be divided into roughly four
generations -
First - 1951 to 1958 - Vacuum tubes - UNIVAC computer.
Second - 1959 to 1964 - Transistors - Higher order languages
/ 1965 to 1970 saw the introduction of the integrated circuit.
/ Instead of large boards, circuits were developed on single
/ chips of silicon. Two devices stand out during this period:
/
Third -< IBM introduced its 360 series mainframe computers and the smaller
\ minicomputer made its debut. Equivalent to a larger computer,
\ but with smaller memory and slower processing, the minicomputer
\ made computers available to the smaller businesses.
Fourth \
The Generations
---------------
The move from World War II to the present can be divided into roughly four
generations -
First - 1951 to 1958 - Vacuum tubes - UNIVAC computer.
Second - 1959 to 1964 - Transistors - Higher order languages
Third - 1965 to 1970 - Integrated circuits - IBM 360 and minicomputers
/ Microprocessors derived from integrated circuits and this
/ put computers on the office desk. Generally thought to begin
/ in 1971 and run to the present, generation four features the
/ microprocessor and derivative personal computer.
/
/ The computers of the fourth generation are roughly 100 times
Fourth -< smaller than those of generation one, yet they are at least
\ as powerful, if not more so.
\
Microcomputers
--------------
The history of computing is like a large tree. Early computing is fairly
easy to trace with few branches to worry about. As you move up the tree
the branches become more numerous and harder to follow. The history of
microcomputers, being fairly high on the tree, is hard to follow with many
related or competing things happening at roughly the same time.
In the 1950's several semiconductor companies were founded to produce
transistors and at least one attempt to design a small computer using
these vacuum tube replacements was made but failed.
The 1960's saw much more activity. In 1968 Intel was founded and in 1969
received a commission to produce integrated circuits for Japanese
calculators. This led to their deciding to build the first microprocessor:
the 4004. Meanwhile, in 1962 Tandy Corporation bought the chain of Radio
Shack electronics stores and Stephen Wozniak (later to found Apple) built
an addition and subtraction machine, winning a prize at a local science
fair. Also, in 1964, John Kemeny and Thomas Kurtz developed the first
version of the BASIC programming language at Dartmouth College.
And, that's just the overview of the period!
Microcomputers (cont)
---------------------
The 1970's took off --
1971 - The 8008 was developed by Intel.
Stephen Wozniak get further involved with computer design.
1972 - The PL/1 programming language for the 4004 written by Gary Kildall.
Traf-O-Data created by Bill Gates and Paul Allen.
Stephen Wozniak and Steven Jobs started selling "blue boxes"
(the blue box was a device for breaking into phone systems).
The People's Computer Company publication was started to make
practical information about computers available to the public.
1973 - Wozniak joined Hewlett-Packard.
An astrology forecasting machine was built by Gary Kildall and
Ben Cooper.
The Community Memory project was started by Lee Felsenstein and
others to allow people access to a public network and see the
power of computers.
Microcomputers (the 70's Continues)
-----------------------------------
1974 - Computer Lib, another computer magazine starts publication.
The 8080 microprocessor is developed by Intel.
A microcomputer and disk operating system by John Torode and Gary
Kildall begins selling.
The July issue of Radio Electronics publishes an article showing
how to build the Mark 8, a computer based on the Intel 8008.
They called it "your personal minicomputer."
1975 - Traf-O-Data has now become Microsoft and develops the first BASIC
for the Altair computer (the Altair was developed by Micro
Instrumentation Telemetry Systems [MITS]).
Popular Electronics publishes an article describing the Altair.
Cromemco is founded.
The Homebrew Computer Club, spawning ground for many ideas found
in today's microcomputers, held its first meeting.
Also, the Amateur Computer Group of New Jersey started.
The Computer Store, the first retail PC store, started in Los Angeles.
The first issue of Byte magazine was published.
The Byte Shop computer store chain was founded in Mountain View,
California.
Micros - The 70's Continues
---------------------------
1976 - IMSAI started shipping its first computers.
Dr. Dobbs begins publishing.
The World Altair Conference was held.
Bill Gates published his "Open Letter to Hobbyists" which spoke to
software piracy (his BASIC, distributed on paper tape, was being
copied without payment).
Wozniak demos the Apple I at a Homebrew meeting.
1977 - The Boston Computer Society was founded.
ComputerLand opened its first franchise store in Morristown, NJ.
Apple Computer opened its first Cupertino office.
The first West Coast Computer Faire is held; for quite a while these
shows became a mainstay of information exchange.
Apple introduces the Apple II.
Commodore builds and distributes the PET.
Tandy/Radio Shack sells its first TRS-80 microcomputer.
We are now to the point where microcomputers started to become available
to the general public and not just "hackers" who were willing to put up
with the unfriendly user interface presented by the first micros.
Closing Out the 70's
--------------------
1978 - Apple began shipping disk drives for the Apple II, making program
distribution much easier.
IMSAI starts to fold because it did not keep up with the technology.
The ogy.
The Lisa development program is started by Apple.
1979 - IMSAI closes its doors after filing for bankruptcy.
Steven Jobs visits the Xerox PARC laboratories and gets ideas for
the Macintosh desktop.
The TRS-80 Model II is announced by Tandy.
WordStar is introduced by MicroPro.
VisiCalc is released by Personal Software.
VisiCalc is largely credited for the microcomputer revolution. This
popular spreadsheet made desktop analysis easy and allowed anyone to write
what amounted to programs without having to learn a complex programming
language. The program was truly a "visible calculator" and took its name
from a shortening of those words. Many Apple II computers were sold for
the sole purpose of running VisiCalc. As each new microcomputer was
introduced, VisiCalc clones were quickly generated for them (for example,
SuperCalc for CP/M computers, Lotus 1-2-3 for IBM, and Excel for Macintosh).
The 1980's
----------
Microcomputer development and sales continued to escalate during the 1980's.
IBM introduced their first PC in 1981 and quickly took over the corporate
marketplace. Apple attempted to make inroads into corporations with the
Lisa in 1982, but the closed architecture (little ability to add features
from other vendors) and other factors caused Apple to eventually drop the
Lisa in favor of their Macintosh line, first introduced in 1984.
IBM-architecture machines (the kind you are running this tutorial on) use
a character interface; the Macintosh uses a graphical interface. Each type
of interface has its proponents and opponents and it's not the purpose of
this tutorial to take sides (so we won't!).
As the 1980's close, versions of past computers based on ever more powerful
microprocessors (the Intel 80386 and Motorola 68030) are quickly giving the
user the power of older minicomputers (and some mainframes) at their desk.
The revolution continues...
The Future
----------
It's hard to predict the future. There are some projections that can be
made, based on extensions of current technology.
Probably the most interesting is the challenge that Japan has issued. In the
early 1980s Japan announced a 10-year program to leapfrog technology a
generation. The outcome is not certain, nor is it completely known, but
one thing we can look forward to is advances in artificial intelligence.
Whether a machine will ever have true "intelligence" is a matter for the
philosophers and theologians. There is no doubt, however, that as computers
get faster and contain more accessible storage, their responses will
become more complete and take on the demeanor of "intelligence."
Without going too far out on a limb, look for smaller and faster...
Introductory notes
------------------
This tutorial gives you basic knowledge about computers and the jargon that
surrounds them. If you are serious about using computers for any task, you
should be prepared to speak the language to others. This tutorial will help.
At the point you first see a term in this tutorial you should mentally
review what you think you know about the term. When you continue, sometimes
after answering a question, the rest of the screen will tell you the
definition and, where appropriate, give some examples. In some cases, added
screens will be used to expand upon the basic definition.
Since some definitions require use of other computer jargon, the more basic
terms will be defined first and then used as building blocks. Therefore,
you should make certain you understand each term before continuing on.
Remember, if you have trouble, go back by pressing -, , PgUp, or move
around with the M (for menu) key. Review until you know the terms (for
quick reviews, don't forget scan mode in the tutorial menu).
OK...Here we go...
What computers do
-----------------
A common misconception is that computers can do anything. Actually, they
are quite limited. Most computers are limited to four mathematical
operations and three comparison operations.
The four basic mathematical operations are:
Addition Subtraction Multiplication Division
+ - * /
The three comparisons are:
Equal to Less than Greater than
= < >
Everything the computer does is done with one or combinations of the above.
Programming ingenuity makes the computer seem "intelligent".
What is the computer best at?
-----------------------------
Many things can be done with a computer; some, however, are more
efficiently done by hand or four-function calculators. In the following
areas, think of what computers can do...then press any key to see examples.
Paperwork Education
Money Health
Commerce Science
Transportation Government
Agriculture Human welfare
What is the computer best at?
-----------------------------
Many things can be done with a computer; some, however, are more
efficiently done by hand or four-function calculators. In the following
areas, think of what computers can do...then press any key to see examples.
Paperwork Education
Repetitive typing/record keeping Record keeping/training devices
Money Health
Banking/cashless economy Business/diagnosis
Commerce Science
Control plants/monitor energy use Data analysis/experiment modeling
Transportation Government
Airline control/rapid transit Everything! - Largest user
Agriculture Human welfare
Crop and weather information Helping disabled/studying society
Hardware versus Software
------------------------
When you talk about computers, you quickly hear the terms: hardware and
software. Make certain you understand the differences.
Hardware Software
Everything you can All instructions and data necessary to make the
put your hands on. computer function. Software is divided into two
subcategories.
Hardware is just what
the name implies, Operating system Applications programs
all physical parts
associated with the
computer. Set of housekeeping Specific set of computer
instructions. The instructions to perform
operating system keeps a given task (like
track of instuctions word processing).
and data in use.
Computer Hardware
-----------------
Computer systems vary widely in how the hardware is configured; what
that hardware does is similar in all systems. The most basic differences
between computer systems are size and use. Below are four different sizes
and their descriptions. Try to match the name to the correct description.
_ Mainframes A. Computers built to minimize distance between
points for very fast operation. Used for
extremely complicated computations.
Microcomputers B. Large computers with fast processing speeds
and access to billions of characters of data.
Minicomputers C. Smallest computers (desk-top and personal).
They are inexpensive and largely owned by
individuals.
Supercomputers D. Moderate sized computer. Used when a desk-top
computer is not powerful enough to do the job.
Please type an answer...You are on try 1 of 3
Division of Hardware
--------------------
The division between different types of hardware is quickly blurring.
While the distinctions made on the previous screen hold true as general
definitions, you will often find hybrids that fill the spaces between
clear type differences. For example, superminis have been developed
with much of the power of a mainframe computer but designed for a single
purpose (e.g. computers designed for processing graphic images).
Microcomputers have likewise grown in power to where the more powerful
could now be called minicomputers using definitions from a couple of
years back.
Computer classification is an art rather then a science. As new
supercomputers are introduced mainframes take on the power of the older
supercomputers. Likewise, as each new microcomputer is introduced it
has the power of the minicomputer of just a few years before.
As computer hardware progresses the desk computer becomes ever more
powerful and can become a better tool if used properly.
Basic Hardware Elements
-----------------------
As indicated previously, all computers, regardless of size, perform
similar tasks. There are five basic hardware elements that perform these
tasks. Following are the five elements and their descriptions.
Input - Some method of getting software into the computer. For a
microcomputer, this is usually a keyboard and storage unit.
Output - Equipment to get data out of the computer. Usually a video
display or printer.
Central Processing Unit - The CPU processes data in response to
software instructions.
Memory - A temporary storage location for software and data. The
memory is cleared when the computer is turned off.
Secondary Storage - Permanent storage for both data and software.
This can be tape, magnetic disk, or other media.
The basic hardware elements described on the previous screen are sometimes
arranged diagrammatically to show how the five interact. That diagram is
shown here.
+------------------+
¦ Secondary ¦
¦ Storage ¦
+------------------+
¦
¦
+-----------+ +------------------+ +------------+
¦ +------¦ Central +------¦ ¦
¦ Input ¦ ¦ Processing ¦ ¦ Output ¦
¦ ¦------¦ Unit ¦------¦ ¦
+-----------+ ¦ ¦ ¦ +------------+
+--+------------+--¦
¦ ¦ ¦
¦ Memory ¦
¦ ¦
+------------------+
Note:
Hardware elements often pass data/instructions to and get instructions
from the central processing unit. For some things, this is not necessary
and those tasks can be given to coprocessors.
Time out for a quiz
-------------------
How many total operations can the CPU perform? 7
Physical parts of the computer are called? HARDWAREt
The conceptual computer is made up of how many elements? 5 e
Let's see if you can name them:
The "heart of the computer" is the......... CPU
This is how things get into the computer... INPUTard
This is how things get out of the computer. OUTPUT
Temporary storage.......................... MEMORY
Permanent storage.......................... SECONDARY STORAGE
Very good. Let's continue on now for some other basic concepts that will
help us tie everything together later.
Coming to terms with time
-------------------------
Shortly, we'll discuss the CPU and other hardware elements in more detail,
but before we start, there are some basic terms you need to know. The
first set of these deals with time.
In the human world, the smallest time element we usually deal with is the
second. Rarely do we need to think smaller.
In the computer world, time increments are much smaller and things happen
much faster. Spell out the fraction of a second each of these represents.
Millisecond - One THOUSANDTH (10E-3) of a second. Associated with smaller
computers and early PC's.
Microsecond - One MILLIONTH (10E-6) of a second. Associated with
minicomputers, some mainframes and most PC's.
Nanosecond - One BILLIONTH (10E-9) of a second. Usually only seen in
supercomputers and newer mainframes.
Picosecond - One TRILLIONTH (10E-12) of a second. A barrier to be broken.
When you eat do you Nibble or Byte?
-----------------------------------
You might do either when you eat, but with computers, each of the above
terms has special meaning in defining how characters are handled by the
computer. Because computers are made up of digital electronics, internally
they respond to two kinds of electrical states: "on" or "off". These may
actually be high or low voltage, or positive and negative voltage, or some
other combination. The key is that there are two conditions. We represent
these with two numbers: 0 and 1, and the arithmetic that deals with these
two states is called BINARY arithmetic.
Each 0 or 1 in the binary system is termed a bit (short for binary digit).
Strings of bits are used to represent numbers larger than 1 (much like
combinations of digits are used to represent numbers larger than 9 in our
decimal numbering system.
Bits in strings of eight are called bytes, and one byte usually represents
a single character of data in the computer.
It's a little used term, but you might be interested in knowing that a
nibble is half a byte (usually 4 bits).
Let's look at the concept of binary numbers and bytes a little closer.
Think of binary numbers in terms of switches. With two switches you can
represent up to four different numbers.
0 0 = Decimal 0 1 0 = Decimal 2
OFF OFF ON OFF
0 1 = Decimal 1 1 1 = Decimal 3
OFF ON ON ON
Study the above for a moment -- it brings out an important concept in
computers. Do you see it?
Look at the decimal number versus the number of numbers. Two binary numbers
gives you up to decimal 3, but there are four actual numbers. In our decimal
system, we rarely think of the zero; with computers, zero is always thought
of as a number.
Thus, a single bit represents 2 numbers, two bits give 4 numbers, three bits
show 8 numbers, four bits represent 16 numbers, and so forth up to a byte,
or eight bits, which represents 256 numbers. (Each added bit doubles the
number of numbers.)
Just to show you the correspondence between binary and decimal numbers
here is a table that runs down a few:
Decimal Binary Binary numbers are formed just like decimal, except
------------------ there are only two numbers to work with. Exhaust
0 ¦ 0 + those two numbers and start over with the next
1 ¦ 1 ¦ position to the left filled with a "1".
2 ¦ 10 ¦
3 ¦ 11 ¦
4 ¦ 100 +-- When you are down to 111 you simply start the entire
5 ¦ 101 ¦ marked series over again with a 1 in front of it.
6 ¦ 110 ¦
7 ¦ 111 + Thus, every time you add a binary digit to the string
8 ¦ 1000 you effectively double the number of total decimal
9 ¦ 1001 digits available for use.
10 ¦ 1010
11 ¦ 1011 Look at the table. One bit counts to two numbers,
12 ¦ 1100 two bits count to four numbers, three bits to
13 ¦ 1101 eight numbers, four bits to 16 numbers, five to
14 ¦ 1110 32, six to 64, seven to 128 and finally, one byte
15 ¦ 1111 (8 bits) counts to 256 numbers.
It is easy to get confused over the point of zero being a digit. A byte
with all digits ON represents the decimal number 255 and it is hard to
visualize this as the 256th digit in a series, but that is exactly what
the computer demands of you.
In brief -- start learning to count from zero, not one!
The first place we will use this concept is in talking about computer
memory. Early manufacturers stated memory capacity in terms of kilobytes.
In the decimal system, the prefix kilo- means 1,000. In the binary system
the prefix kilo- means what?
It's a little tricky, but it means 1,024, the closest number of digits to
1,000 that can be represented by a number of bits that are all set to one.
That number is 10. Thus, ten ones in a row represents the decimal number
1,023 and the 1,024th digit. Using this nomenclature, a computer may be
described as having 640K (640 kilobytes) of memory, when it really has
640 x 1,024 or 655,360 bytes.
By the same token, computers are described as having megabytes and
gigabytes of memory, even though there is somewhat more than a million
or billion actual bytes available.
Addressing
----------
To understand addressing, think of each memory location as a post office
box containing one character (letter, digit or special character). Each box
has an "address" that makes it unique.
You should already know how many boxes an 8-bit binary number can specify.
Just as a review, how many? 256 boxes, that's right.
How many do you think a 16-bit binary number can specify? 65536
You have a real grasp of the material. Let's see how that number comes
about.
Think of memory as a series of 256 pages, each containing 256 bytes of
information. This is what a 16-bit number can address. Multiply 256 x 256
and you get 65,536 -- exactly 64K.
Of course, the maximum amount of memory that any computer can have will
depend upon how many bits the CPU has in its address bus (that's the wires
the CPU uses to send out addresses, not a local RTD line). Early computers
had a 16-bit bus or 64K memory, later computers have a larger bus for more.
The CPU in detail
-----------------
You've seen the Central Processing Unit (CPU) in its role of control
center for the computer. It carries out all instructions sent to it by
the operating system or applications software. Now let's look at the
device itself to see what makes it do its job.
The CPU contains two circuit elements that perform tasks and several
memory locations where data/instructions are held temporarily while actions
are performed.
Here they are:
Control Unit - Directs and coordinates all elements of the computer.
The control unit does NOT do, it only DIRECTS.
Arithmetic/Logic Unit - This is the unit where the seven basic math-
ematical and logical operations you learned
about earlier take place.
Registers - Temporary storage locations.
Registers
---------
As pointed out, these are temporary storage areas within the CPU that are
used when data must be manipulated or instructions carried out. You will
usually find at least four registers, and often more. The most common are:
Accumulator - This register is used to "accumulate" the results of
calculations.
Storage - A holding area for information taken from or to be sent to
memory.
Address - Holds the location of information or instructions the computer
needs for processing.
General Purpose - Can be used for multiple functions to include arithmetic
or addressing.
Registers vary in length (number of bits) with the computer. Personal
computers have 8- or 16-bit registers, larger PC's are 32-bits, and
minis/mainframes have up to 64-bit registers. This length is commonly known
as a word and the longer it is, the more powerful the computer. Sometimes
the registers have different lengths, depending on their use.
The basic operation of the CPU can be summarized with the following diagram.
(Assumed computer word size is 8-bits with 16-bit address line, like a 64K
personal computer.)
+--------------+ +------------------------------+
¦ Memory +-------------------------+ Central Processing Unit ¦
¦ 16-bit address line ¦
¦- - - - - - - +-------------------------+ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦
¦ Operating +-------------------------+ ¦
¦ system Commands ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦
¦ +-------------------------+ Registers ¦
¦ Program +-------------------------+ ¦
¦ instructions Instructions ¦
¦ +-------------------------+ ¦ Control Unit ¦
¦- - - - - - - ¦ ¦-¦- - - - - - - - - - - - -¦- ¦
¦ Stored ¦ ¦ Arithmetic/logic Unit ¦ ¦
¦ data +-------------------------+ ¦
¦ Data ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦
¦ +-------------------------+ ¦
¦ ¦ Commands & instructions ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦
¦ ¦ flow to the CPU and data¦ Registers ¦
+--------------+ is moved back and forth.+------------------------------+
All information needed is addressed by the CPU as is all transfer to/from
memory.
PgDn + next screen PgUp - prior screen ESCape to end M for menu
Today's CPUs
------------
CPUs in personal computers have moved from 8-bit to 32-bit and show every
sign of not slowing down. The amount of memory each can address has also
gone up with each generation, from 1 megabyte for early micros to four
gigabytes (remember, that's BILLIONS), and growing.
For microcomputers, the most common CPUs are built by Intel. Early models
were the 8088 and 8086, an intermediate model is the 80286, and current
models are the 80386 and i486. New generations typically are introduced
about every 18 months so the 586 and 686 are not far behind. (The most
popular alternatives to Intel CPUs are built by Motorola and are the
68000, 68020, 68030, and 68040; used in Apple Macintosh and other
computers.)
Expect new CPUs to continue to be smaller and faster.
Also, as chip-making technology advances you can expect to see other parts
of the computer integrated onto a single chip with the CPU. The functions
are all there, just in a smaller package.
Let's rest now!
---------------
You've been a patient student to this point. No sense in burning you out.
Take a break, after all you've learned about such things as:
The seven basic computer operations.
What the difference is between hardware and software and what makes up
software.
The names given to computers of different size and what they are used for.
All five basic hardware elements and how they are generally related.
How the computer thinks of time.
The difference between bits and bytes, not to mention kilo-, mega- and
gigabytes.
Zero is a number!
The concept of addressing.
A word is not necessarily something you read in a book.
What makes up the CPU and its registers, and how these are all related.
What's that -- you don't think you learned all that? Best go back through
after a break then. Otherwise press on to part 2 of this series and learn
more about input/output and storage...
Operating systems
-----------------
The operating system on any computer is the housekeeper for that computer.
It manages the files and data throughout the system and serves as the
interface between you, your program and the rest of the computer. Most
anything you do with the computer will be done through the operating system.
In personal computers you usually find certain generic operating systems,
that is versions of the same operating system built for different sets of
hardware to allow a programmer to have a standard set of commands to do
similar things on different machines.
PC-DOS, the disk operating system for the IBM-PC computer is a version of
the more general MS-DOS, developed for 16-bit microcomputers. OS/2 and
UNIX are two other operating systems for more advanced microcomputers.
The tutorial will offer descriptions and examples.
You will be asked to type some of the DOS commands during this tutorial.
DON'T WORRY...the tutor program has control of the computer and you will
not actually execute the commands.
Parts of DOS
------------
DOS consists of an input/output system, a command processor and several
utilities. The utilities are individual program files found on your DOS
disk. While part of DOS, these files are not needed often enough to make
it necessary or practical to keep them in the computer's RAM all the time.
FORMAT.COM, the program that formats blank disks is an example of a DOS
utility. Sometimes these utilities are called external commands.
The command processor is also a file you see on the disk, but once read
into the computer's memory, it usually resides there. Some programs
provide their own command processor, and there are times when the command
processor will be overwritten by a program and have to be reloaded when
the program stops executing.
The input/output system consists of two files and a ROM chip. While the
two files are on your disks and are loaded into memory when the computer
starts, they are normally hidden from your view and not available to
you for changing.
Input/Output system
-------------------
This most primitive of the DOS systems has two parts:
BIOS (Basic Input/Output System)
These are the fundamental routines that control the keyboard, video
display and other peripherals.
The BIOS is comprised of a ROM on the computer's main circuit board
and the file IBMBIO.COM, one of the two hidden files on your disk.
Operating system
This is the main file-handling system for the computer. Actually, two
systems exist: one for disk-based files and one for non-disk peripheral
devices. They are in hidden file IBMDOS.COM. (IBMBIO and IBMDOS are
IBM names; MS-DOS uses IO.SYS and MSDOS.SYS.)
The two systems are necessary because non-disk peripherals demand their
data as strings of characters, while disks move information in large
groups, known as blocks.
Command Processor
-----------------
The command processor (the file COMMAND.COM on your disk) performs
three major tasks:
It handles critical interrupts...that is, COMMAND.COM takes care of all
demands for attention by parts of the computer. The user typing the
Control-ScrollLock program break command is an example of an interrupt.
It handles critical errors...that is, COMMAND.COM takes care of problems.
For example, if you leave the disk drive door open during a disk operation
COMMAND.COM is responsible for the error message you will see.
It performs end-of-program housekeeping...that is, COMMAND.COM takes care
of making the computer's memory available for other programs and reloading
parts of itself if the program wrote over them.
COMMAND.COM also places the C> prompt on the screen and interprets any
command(s) you might type. In short, the command processor tells the rest
of DOS what to do.
Starting the computer
---------------------
The process of starting a computer is given a special name. Do you know
what it is? BOOTING As you can see from the process described below
when you start a computer it literally picks itself up by its bootstraps,
thus resulting in this otherwise strange term. When you turn on the power
the computer first checks its memory and some other components. After this,
the left (or top) disk drive will begin to spin and the boot process will
commence. Follow the steps below:
1. ROM BIOS loads Track 0, Sector 0 of the disk. This sector contains a
short program that can read the rest of the input/output system.
2. The boot loader read in step 1 loads the input/output system (files
IBMBIO.COM and IBMDOS.COM [or IO.SYS and MSDOS.SYS]).
3. IBMBIO.COM initializes the hardware of the computer, runs the file
CONFIG.SYS (if found on the disk) and then moves IBMDOS.COM into its
proper location in RAM.
4. IBMDOS.COM loads COMMAND.COM and turns control over to it. COMMAND.COM
runs the file AUTOEXEC.BAT (if found) and then command is given to you.
Default drive
-------------
The default drive is the disk drive on which PC-DOS will look for a program
if no drive specification is given with the filename.
How do you know what it is? Look at the prompt. The default drive
letter is part of the prompt.
A> indicates that drive A (the left or top drive in a two-drive system)
is the default drive.
The right (or second) drive in such a system is called drive B and the
hard disk in any system is usually given the letter C as its drive
designation.
DOS supports many more than drives A through C. In fact, if your computer
has them you can specify up to 63 drive names. You change drives by
typing the desired default drive followed by a colon at the prompt. To
change to drive C type what?
A>C: You'll see C> as the new system prompt.
Device names
------------
Character oriented devices can be addressed by DOS through their names.
Each device has a unique name as described below:
CON: The name for the video display and keyboard.
AUX: or COM1: This is the first asynchronous communications port which
usually has a modem or other serial device connected to
it. The second communications port is COM2:
PRN or LPT1: The first parallel printer port. PRN comes from printer
and the LPT is an old designator derived from line
printer. A colon on PRN and all device names is optional
in later DOS versions. The second parallel port is LPT2:
CAS1: A holdover from the early days of personal computers,
this is the cassette recorder port.
NUL: This is a test device. Anything sent to device NUL: goes
into the bit bucket (i.e. gets thrown away).
Rules for filenames
-------------------
Like devices, disk files have to be identified so DOS can address them.
These filenames have specific rules as shown here:
Filename.ext
/ \
/ \
This is the root name This is the extension.
and can be from 1 to It is optional, but if
8 characters in length, used is 1 to 3 characters
and not a device name. long.
The period is used between the filename and extension
and must be present if there is an extension.
The following are legal and illegal characters in a filename or extension:
Legal Illegal
----- -------
A-Z 0-9 $#&@!()-{}'`_~ |<>\^+=?/[]";,*
Control characters and the space
DOS commands
------------
DOS commands are issued at the prompt A>. Whatever you type after that
prompt that is not in the COMMAND.COM standard library is assumed to be
the name of a file on the default disk and DOS will search for it under
one of three names (in the order listed).
If you type A>FILENAME
DOS will look for: FILENAME.COM or
FILENAME.EXE or
FILENAME.BAT
The first is a command file (note the COM extension). The second is an
execution file (EXE extension). And, the third is a batch file (see the
Batch Files tutorial). The first file found will be read into the
computer's memory and the command processor will start the program running.
Both .COM and .EXE files execute as programs. The difference between the
two relates to how memory is allocated and certain parameters in the
computer are set.
Command syntax
--------------
Each DOS command has a mandatory part and some have an optional part.
In color, the mandatory parts will be shown in bright red CAPITAL LETTERS
and the optional parts in lower case cyan. In monochrome the mandatory
parts will be brighter.
For example, DIR d:pathname\filename.ext/p/w
is the complete command for a disk directory. Note that only DIR is
necessary.
You may note the new term pathname in the above command. Floppy disk users
should not worry about this term and hard disk users will have it explained
in the advanced DOS tutorial. For now, we will simply ignore it in all
commands.
In some commands you may use wildcards. A wildcard, like the joker in a
card deck, can stand for any character or group of characters.
The ? represents any single character FILE? = FILE1 or FILE2 etc.
The * represents any group of characters *.* = Any file and ext
Disk directory
--------------
To see a listing of what is on a ¦ A>DIR
disk, issue the DIRectory command. ¦ Volume in drive A has no label
¦ Directory of A:\
It comes with several options. ¦
¦ COMMAND COM 17664 3-08-83 12:00p
DIR d:filename.ext/p/w ¦ FORMAT COM 6016 3-08-83 12:00p
¦ ...
DIR alone will show the complete ¦ BASICA COM 25984 3-08-83 12:00p
directory. With the optional ¦ 41 File(s) 83968 bytes free
filename, DIR will try to find ¦
just that file. ¦ Note several things here.
¦
The /p option causes a pause when ¦ DIR tells you what files are on the
the screen fills. ¦ disk, how big they are, and when
¦ they were created.
The /w option yields a full ¦
80-column display of just the ¦ Finally, DIR tells how many files
filenames. ¦ total are in the list and what free
¦ space remains.
Try it now...type DIR at the prompt. ¦
Three simple commands
---------------------
CLS Clears the screen and puts the cursor in the home (upper left)
position.
VER Shows the DOS version number on the video display. You are shown
the one-digit version and two-digit revision.
VOL d: Displays a volume label, if one exists. The label is a name you
have given to the disk when it was formatted. It is used for
identification purposes.
------------------------------------------------------------------------------
Issue the VER command (type VER and Carriage Return):
A>VER
IBM Personal Computer DOS Version 3.10
Issue the VOL command (type VOL and Carriage Return):
A>VOL
Volume in drive A is MYDOS3.1
Issue the CLS command (type CLS and Carriage Return):
A>CLS
Date and Time
-------------
These two commands show and/or set the system date and time. When
the computer boots you are expected to set these (or have software
and a clock card that sets them for you). If you don't, the default
values will be 1-1-80 for the date and 00:00:00.00 for time.
You can enter the date as month/day/year with hyphens or slashes, i.e.
3/1/85 or 3-1-85 are acceptable dates
Do not enter the day of the week, even though it shows on the screen.
The computer will calculate it for you. A two digit year assumes dates
between 1980 and 1999. In 2000 you will have to start putting in all
four digits.
The time setting requires a 24-hour clock, i.e. any time after noon has
to have 12 added to it, for example 3:00 pm has to be entered as 15:00.
(On some computers these commands will change the permanent settings.)
------------------------------------------------------------------------------
A>DATE A>TIME
Current date is Tue 1-1-1980 Current time is 00:00:00.55
Enter new date: 1-23-85 Enter new time: 21:28
Format disk
-----------
Disks straight out of the package ¦ Problem: Format the disk in drive
need to be formatted, that is ¦ B: with the DOS system.
have tracks and sectors defined ¦ Issue the proper command.
so DOS can find programs and ¦
data on the disk. ¦
¦ A>FORMAT B:/S
FORMAT d:/s/1/8/b/v ¦
¦ Insert new diskette for drive B:
where ¦ and strike any key when ready
¦
d: defines where the disk is ¦ Formatting...Format complete
/s puts the DOS system on disk ¦ System transferred
/1 formats one side only ¦
/8 formats as 8 sectors per ¦ 362496 bytes total disk space
track for use by DOS 1.1 ¦ 40960 bytes used by system
/b formats as 8 sectors per ¦ 321536 bytes available on disk
track and leaves room for ¦
the DOS system ¦ Format another (Y/N)? N
/v puts a volume label onto ¦
the disk for identification ¦
Additional Comments
-------------------
Some microcomputers have 1.2 megabyte 5.25" disk drives. There is the
temptation to use 360 kilobyte disks in those drives -- don't do it. The
track width is smaller and if you then put the 360K disks into a 360K
drive, they may not work properly. Likewise, you cannot use the high
density floppy disks themselves in 360K drives. The magnetic properties
of the disk are such that the 360K drives won't format them.
With the introduction of 3.5" drives, higher versions of DOS are required
to correctly support the new formats. The 3.5" drives come in two sizes:
720K and 1.4MB. Unlike the 1.2MB/360K drives disks, it is possible to format
to 720K in a 1.4MB 3.5" drive. All you have to do is tell the FORMAT command
the track/sector combination you need:
FORMAT A: /N:9/T:80 (this tells DOS to set 9 sectors/track and
80 tracks for a total of 720 Kilobytes)
Not all versions of DOS support higher capacity disks. For example, DOS
3.2 introduced support for 3.5-inch disks, but only at 720K format. In
order to format a 3.5-inch disk at 1.44MB you will need DOS 3.3 or later.
Erasing files and Renaming files
------------------------------------------------------
---
Files you no longer need should be ¦ For whatever reason, you may need to
deleted from your disk to make room ¦ change the name of a file on your
for more current files. Use the ¦ disk. (Usually this is the case when
ERASE (DELete) command for this: ¦ you want to change a backup file to
¦ another name in order to return it
ERASE d:FILENAME.ext ¦ to active status.)
or ¦
DEL d:FILENAME.ext ¦ Use this format:
¦
Be careful, typographic errors in ¦ REName d:OLDNAME.ext NEWNAME.ext
this command can bring disaster! ¦
¦ Wildcards are allowed, but can
You are allowed to delete all files ¦ cause trouble if you are not
on a disk with the wildcard * ¦ careful.
(ERASE *.*), but DOS will question ¦
you. ¦ The rename command will give you an
¦ error message if NEWNAME exists.
Recovery BEFORE writing anything ¦
else to disk is possible, but NOT ¦
with a DOS utility. ¦
---
Copying files
-------------
The COPY command is a very powerful command within DOS. With it you can
create duplicates of individual files, join several files into one, and
even use your computer like a simple typewriter by "copying" from the
device named CON: to the device named PRN (inefficient, but OK for short
notes).
Copying one file to another (copys from filename1 to filename2):
COPY d1:FILENAME1.ext d2:filename2.ext/v
/v option verifies the copy as it takes place. This adds confidence
at the price of slower operation.
There are other options beyond the scope of these tutorials.
Wildcards are allowed. (See your DOS manual.)
------------------------------------------------------------------------------
A>COPY ADDRS.LST B: Copies the single file ADDRS.LST from A: to B:
A>COPY *.* B:/V Copies all files on A: to the disk in B: and verifies
A>COPY ADDRS.LST Yields an error message. Can't copy a file to itself
A>COPY B:*.* Copies all files from drive B: to drive A:
Copy can also be used to concatenate (join) several files by using the
following form:
COPY d1:FILENAME1.ext+d2:FILENAME2.ext+... d0:filename0.ext/v
The options are the same as the previous version of the copy command.
All specified filenames (#1, #2, etc.) will be copied and joined into
filename0. If no filename0 is specified, the first source file named
will be used.
Wildcards are dangerous with this command.
------------------------------------------------------------------------------
Example:
Contents of FILE1: This is file number one
Contents of FILE2: This is file number two
A>COPY FILE1+FILE2 FILE3
Contents of FILE3: This is file number oneThis is file number two
The COPY command can be used to create text files by copying from device
CON: to a file. The procedure is outlined in the text of the example
below.
A>COPY CON: TEXTFILE
This is the text to go into the text file being created.
Each line is typed to the screen and it is being saved into
a buffer for later transfer to the file TEXTFILE. Each line may
be corrected as it is typed, but cannot be changed after it is
terminated by the carriage return. Also, if you happen to type
beyond column 80 on the screen, you cannot correct anything on the
line above. Each line must be terminated by a carriage return
(the enter key). You signal you are finished by typing a
Control-Z, the symbol for end-of-file, followed by Return.
^Z
1 File(s) copied
XCOPY
-----
For copying multiple files the XCOPY command can be a powerful ally. As
its name implies, the command performs extended copies. Its format:
XCOPY d1:PATH1 d2:path2 /a /d:date /m /p /s /v /w
Like the COPY command, XCOPY can take a single drive/path designator in
which case files from that destination will be copied into the current
directory. Some options:
/A Copy only files with archive bit set; do not reset archive bit.
/D:date Copy only files with specified date or later.
/M Copy only files with archive bet set; reset archive bit.
/P Prompt before writing target file(s).
/S Copy subdirectories as well unless they are empty.
/V Verify copied files as they are written.
/W Wait for keypress before starting to allow disk change.
You can copy an entire hard disk to another disk with a single command:
XCOPY C: D: /S. The contents of drive C: will be copied to drive D: a file
at a time, with the subdirectory structure intact.
Typing a file
-------------
Any text file saved in ASCII character format can be easily seen on your
video display. Use the type command:
TYPE d:FILENAME.ext
All characters in the file will be displayed on the screen, including any
control characters, sometimes resulting in some interesting displays.
Any control-I characters found will be interpreted as a tab, and spaces
will be added to get the cursor over to the next 8-character boundary, so
some output may appear as tables. A Control-Z will cause output to stop.
Attempting to TYPE a .COM or .EXE file will result in garbage on the
screen, and should generally be avoided.
Backing up a disk
-----------------
Disks wear out after several hundred spin hours. Well before that time
you should have made a copy of the disk to preserve the integrity of its
contents. You can, of course FORMAT and then COPY *.* to accomplish this.
There is a quicker way however:
DISKCOPY d1: d2:/1
/1 will force copying of side 0 of the disk only, regardless of how it
was recorded.
If you do not give drive specifications, the utility will ask for them.
All information on the target disk will be destroyed, and DISKCOPY will
format the target if it is found blank. Be careful, it's easy to destroy
data by putting the disks in backwards!
------------------------------------------------------------------------------
Problem: Copy disk A: to B:. Issue the proper command.
A>DISKCOPY A: B:
Checking the disk
-----------------
Now and again it is useful to check the integrity of the disk directory and
file allocation table (FAT). The FAT is so important to the disk that there
are two copies of it on each disk.
CHKDSK d:filename.ext/f/v
Using the filename causes it to be checked for continuity (i.e. being stored
on contiguous sectors on the disk for more efficient access).
/f tells DOS to automatically fix the FAT and other problems
/v is a verbose mode that shows progress as disk checking is taking place
------------------------------------------------------------------------------
A>CHKDSK
Volume MYDISK created Feb 3, 1985 7:58p
362496 bytes total disk space
22528 bytes in 3 hidden files +--------------------------------+
316416 bytes in 42 user files ¦ Only use the version of CHKDSK ¦
512 bytes in bad sectors ¦ that came with your version of ¦
23040 bytes available on disk ¦ of DOS. Crossing versions can ¦
131072 bytes total memory ¦ cause great damage to a disk. ¦
106064 bytes free +--------------------------------+
Notes
-----
You should understand what makes up DOS, what constitutes a file and know
how to run several useful DOS commands. By no means have you seen all DOS
commands. Some of the commands you may need in special circumstances should
be looked up in the DOS manual. By now you should be able to do that and
understand what is said. Following are a few of the more interesting to
look up.
COMP d1:filename1.ext d2:filename2.ext
Compares two files for the purpose of identifying identical copies.
DISKCOMP d1: d2:/1/8
Compares two disks, track by track. Mostly used after DISKCOPY.
SYS d:
Puts DOS (IBMBIO.COM and IBMDOS.COM) onto the target disk.
PROMPT promptstring
Changes the prompt from A> to whatever you want.
Introductory comments
---------------------
In the Introduction to DOS tutorial you learned the basics of files and
DOS commands. Recall that many of these commands had filenames as either
part of the command or an option to the command.
Given the limited capacity of floppy disks, this rarely posed a problem.
To find the necessary filename all you have to do is call up a DIRectory.
For hard disks, however, with their large storage capacity, a directory
listing could take considerable time to complete if you had to go through
each and every filename on the disk.
The solution that Microsoft came up with in their DOS 2.0 or later is
the addition of pathnames.
As the name implies, a pathname is nothing more than a "path" that directs
DOS to your particular file.
You see, with DOS 2.x, IBM/Microsoft introduced multiple directories on
a single disk. In effect, this lets you sort your files into groups and
place each related group into its own directory. This means that you
don't have to search an entire disk to find one file.
Subdirectory
------------
What do you think a lower-level directory is called? SUBDIRECTORY
Of course...would we try to trick you? (Don't answer that!)
Seriously, consider a disk. To this point you have learned that each
file on that disk is represented as an entry in the directory, put there
so both you and DOS can find the file on disk.
If, instead of data, you created a file that pointed to other files on
the disk, you will have built what amounts to a subdirectory.
DOS manipulates files in subdirectories through several directory
commands and what is called a pathname.
In this section we'll look at the DOS commands for manipulating
subdirectories and how we can set an environment variable (PATH) to
allow DOS to find programs.
Let's look first at how DOS organizes subdirectories.
Tree structure
--------------
The DOS directory structure can be thought of as a tree, with the master
disk directory being called the ROOT and subdirectories thought of as
branches. The root is the hard disk's master directory. It may contain up
to 512 entries. Subdirectories may contain any number of entries (until the
disk is full). A floppy root directory may contain 112 or 224 entries.
A: ¦ SUBDIR1 ---------------+ ¦ FILE9 ¦ FILE15
¦ ¦ ¦ ¦
¦ SUBDIR2 --+ +---------¦ SUBDIR4 --------------¦ FILE16
¦ ¦ ¦ ¦
¦ FILE1 ¦ ¦ FILE10 ¦ FILE17
¦ ¦ ¦
¦ FILE2 ¦ ¦ FILE6 ¦ FILE11
¦ ¦ ¦ ¦ FILE12
¦ FILE3 +----¦ FILE7 ¦
¦ ¦ ¦ FILE13
¦ FILE4 ¦ SUBDIR3 --------------------------¦
¦ ¦ ¦ FILE14
¦ FILE5 ¦ FILE8
Tree structure
--------------
In the example below, there are five files and two subdirectories in the
root. Each of the subdirectories has similar contents. SUBDIR1, for
example, has three files and one subdirectory in it. This structure can be
extended until the disk is completely full, subject only to the constraint
of 63 characters for the pathname that you will use to find a particular
file.
A: ¦ SUBDIR1 ---------------+ ¦ FILE9 ¦ FILE15
¦ ¦ ¦ ¦
¦ SUBDIR2 --+ +---------¦ SUBDIR4 --------------¦ FILE16
¦ ¦ ¦ ¦
¦ FILE1 ¦ ¦ FILE10 ¦ FILE17
¦ ¦ ¦
¦ FILE2 ¦ ¦ FILE6 ¦ FILE11
¦ ¦ ¦ ¦ FILE12
¦ FILE3 +----¦ FILE7 ¦
¦ ¦ ¦ FILE13
¦ FILE4 ¦ SUBDIR3 --------------------------¦
¦ ¦ ¦ FILE14
¦ FILE5 ¦ FILE8
Tree structure
--------------
The rules for a subdirectory name are just like that for filenames (eight
characters followed by a period and three character extension).
They show up in a directory listing with the designator behind them.
Let's see now how to build a pathname.
A: ¦ SUBDIR1 ---------------+ ¦ FILE9 ¦ FILE15
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