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IF YOU HAVE NEVER USED A COMPUTER BEFORE:
Welcome! Computers have been around since the Chinese Abacus.
They are here to stay. There is a certain feel and flow to the
logic which directs their activities.
Electronically all computers work about the same. The one you
are using is called a MICROcomputer. This is due to its size.
Larger computers include MINIcomputers and Mainframe computers.
RAM
---
Think of a computer as a human brain. Your brain is a memory sponge.
It contains a lifetime of memories which cause us to act or react
based on inputs. Inputs come via our 5 senses. If you see and smell
a steak burning on the grill (inputs) you know how to react based on
previous experiences (memory - go out to eat).
The computer's brain is comprised of a large memory area called Random
Access Memory (RAM) and a calculating portion called the Central Processing
Unit (CPU). The CPU and RAM work together as the computer's "brain". Each
day when we start up the computer one of the first tasks will be to fill
RAM with instructions to give it an ability to perform work. This work may
be in the creation of documents or tracking accounting data (more information
on CPU is found under the HARDWARE section).
You control which instructions will go into the computer's brain.
You control which sets of experiences you will provide the
computer. Once in RAM, the computer will evaluate inputs from
many devices and react. The most typical input device is a
keyboard. As you type commands, the computer evaluates them and
based on the set of instructions within its RAM, will follow some
action - perhaps print a document, calculate, or send information
over a telephone line.
At some later point you may empty the computer's brain and
install a different set of instructions, thus giving it a
different ability.
Unlike a human, the computer requires electricity to keep the
information within RAM. Each time the computer is turned off,
all information within RAM is lost. RAM is a temporary memory.
To save instructions for use at a later date, a storage device is
required. Computers use many such devices. Your computer uses a
Floppy Disk and/or a Hard Disk. Both are similar.
DISKS
-----
Think of these disks as cassettes. You can record information on
a cassette which can be replayed indefinitely and if desired,
recorded over. Floppy and Hard Disks operate in a similar fashion.
We record (Save) something we have created - like a document - onto the
disk. Then, hours, days, or months later we are able to play back
(Retrieve) the document into the computer to alter or print out. Just
like cassettes, the Floppy and Hard Disks do not require electricity to
retain their information.
Hard Disks and Floppy Disks are similar. Hard Drives have a larger
capacity for file storage, are faster and are less likely to fail due
to the protected environment from within which they operate.
RAM is called volatile memory because of the electricity
requirement. Floppy and Hard Disks are called non-volatile
memory because they will retain their information without the aid
of electricity.
A computer system includes computer hardware, software and
people. A computer is a device capable of solving problems
or manipulating data by accepting data, performing prescribed
operations on the data, and displaying the results.
HARDWARE versus SOFTWARE
------------------------
HARDWARE: Physical equipment such as electronic,
magnetic, and mechanical devices (monitor, keyboard,
printer, microchip boards,...). Includes INPUT/OUTPUT
DEVICES which allow the operator to communicate with the
computer and vice versa.
SOFTWARE: Sets of programs (stored sets of
instructions) that govern the operation of computer system
and make the hardware run. These programs (instructions)
tell the hardware how to perform a particular task such as
word processing, games, database management, etc.
Software refers to the instructions that are used to enable
an otherwise dead machine to understand your inputs and
transform them into desired outputs.
Computer hardware by itself has no personality; this is
determined by the software. Word processing software turns
the computer into a word processor, accounting software turns
the computer into an accounting tool, etc.
The computer requires two types of Software:
DOS - Disk Operating System
Application Software - Word Processing, Spreadsheet, Games,
Database Management, Accounting, Payroll, etc.
DOS (Disk Operating System)
---
All computers require an operating system and the one IBM
PC's use is referred to as DOS (sounds like floss). DOS is
software that allows the terminal, printer, computer and mass
storage systems (floppy disks) to work together as a unit,
and controls the execution of programs. It also allows you
to perform housekeeping chores in regards to managing disks
and files.
Therefore - DOS: 1. Links Hardware
2. Enables File Management
PROPER HANDLING OF DISKS - DISKS NEED CARE!
------------------------
- Never touch the mylar surface - Do not bend the disks
- Always store in their protective sleeve
- Hold the disk by its label or any part of the sleeve
- Avoid bringing disks near magnets (TVs, telephones,..)
- Do not leave in hot or cold areas (radiators, car-dash, in
car during winter, etc.)
- Use felt tip pens if possible when labeling. Ball points
can crease the mylar.
Note the write-protect notch on the disk. If this is covered
by tape or non-existent, data cannot be "written" to the disk.
However, data can still be "read" from the disk.
It is a good idea to always save data and programs on two
separate disks in case one is destroyed. Even with the most
cautious of care, the delicate Floppy Disks sometimes fail
for no apparent reason.
HISTORY:
The first computational device was the abacus. This has been
in continuous use for thousands of years. During the 1600's the
Pascal adding machine was developed. This was a mechanical
device which laid the groundwork for today's odometers and
gas meters. The 1800's saw many machines developed that were
controlled by punch cards - weaving looms, etc. The
theoretical basis for electronic circuitry was developed in
the mid 1800's.
The first electronic computer was developed in 1942 at Iowa
State College. From this point forth there were numerous
firsts as computers became less mechanical, smaller, faster
and cheaper. IBM began dominating the computer market by the
mid-1950's and still does today in the mainframe (very large
computer installation) market. Digital Equipment Corp.
(DEC) became a significant competitor by the mid-1960's. DEC
is generally considered technically better (faster, smaller,
etc.) than IBM but still only has a fraction of the total
market due to marketing snafus. Today the Cray Supercomputer
is the fastest in the world, is manufactured in Wisconsin,
and is set in a vat of liquid helium to increase the
conductivity for faster operation.
TIME vs SPEED
Method of Calculation Approximate Speed
Human (manual calculation) 1 each 60 seconds
Burroughs E101 (1954) 4 per second
IBM 1130 (1964) 600,000 per second
DEC PDP 11 (1974) 1,000,000 per second
Cray supercomputer 13,000,000 per second
The Personal Computer is defined by its size, cost
applications for small business and the home. The first one
appeared in January 1975 and was the Altair 8800 kit. Only
hobbyist bought these. Then the Radio Shack TRS 80 and Apple
computers hit the market as the first pre-assembled
microcomputers.
Market growth remained sluggish until two business students -
Dan Bricklin and Dan Fylstra developed a program to run on
Apple computers to handle the tedious recalculations in their
school assignments. This program was called VisiCalc and is
the forerunner to the spreadsheet program Lotus 123.
With VisiCalc as a useful tool, Apple sales took off. Apple
became the standard because all programs were written for
Apple. Today we still see Apple dominate the school market.
In 1981 IBM introduced its PC which is unable to run Apple
software. Unlike Apple or other IBM products, the IBM PC had
an open architecture which means the technical details of how
it operated were published right along with the product's
introduction. This permitted hundreds of companies to write
software (programs) for the IBM PC as well as a variety of
accessories. Adding IBM's sterling reputation, the open
architecture did enable rapid market penetration. The
microcomputer was no longer a toy, it was a business tool.
The open architecture however, also allowed for the
generation of a host of lower cost compatible computers.
IBM had traded quick initial market entry for eventual erosion
of market share. In both instances, we the consumers
benefit.
HARDWARE:
CENTRAL PROCESSOR UNIT (CPU): Heart of the PC - it contains
the microprocessor. The CPU is a set of miniaturized circuits that
does all the "thinking". It controls the interpretation
(arithmetic-logic unit) and execution (control unit) of instructions.
It is this CPU in conjunction with RAM that comprise the computer's
"brain". The CPU does the "thinking/calculating" while RAM contains
the instructions or "memories". It is the CPU that largely determines
the operating speed of the computer.
BIT: Smallest unit of information recognized by the
computer. BIT is short for Binary Digit. A Binary Digit can
be either a 0 or a 1. Several bits make up a byte.
BYTE: A group of 8 BITS. This grouping of adjacent binary
digits (bits) is operated on by the computer as a unit.
Computers use 1 BYTE to represent 1 character such as a
letter of the alphabet, a number, a punctuation mark, a
space, etc. A BYTE is also a unit of measure since it
represents 1 character. For example, when the letter "A" is
pressed, the keyboard actually sends the following to RAM:
10000001 - a set of 8 bits. See RAM, FLOPPY DISK.
RANDOM ACCESS MEMORY (RAM): A set of miniaturized circuits which
represents the working memory of the computer. This is where
application programs (software) can be loaded from the outside and then
executed. The larger the RAM the better. A typical single-user
computer system may contain approximately 640,000 bytes of RAM. (This is
often abbreviated as 640k RAM: 1 k bytes is actually = 1024 bytes)
The RAM is emptied when the computer is turned off - thus it is
often called "volatile" memory. WHAT YOU SEE ON YOUR COMPUTER MONITOR
IS ACTUALLY IN RAM ONLY - a temporary storage location. To make it
permanent we "save" it, or "write" it to a floppy disk or hard drive.
These devices are not volatile storage - they do not require
electricity.
READ ONLY MEMORY (ROM): This is a special section of memory
that contains instructions which are activated each time the
computer is turned on. These instructions are set at the
factory and cannot be changed - thus, they can only be "read"
not written to. ROM instructions perform equipment checks
and initialization of the computer prior to each use.
DISK DRIVE: The port in which a floppy disk is inserted. Device that "reads"
data from a magnetic disk and copies it into the computer's memory (RAM) so it
can be used by the computer, and that "writes" data from the computer's memory
onto a disk so it can be stored for later use. Each Disk Drive is labeled
A,B,C,etc because we often must tell the computer which drive has the disk
with the information or where to send the information. A Disk Drive reads and
writes on a 5.25 inch or 3.5 inch floppy disk.
FLOPPY DISKS: The most commonly used mass storage device. Allows
entering programs to RAM and saving data from RAM. Will hold data even
after the computer is turned off. Data on these disks is stored in
concentric rings called tracks. The Disk surface is a thin piece of
mylar and is coated with a magnetized material similar to audio or
video tape.
The read/write heads can magnetize and demagnetize the coated surface
repeatedly. Therefore, the Disk can be used, erased, and reused
indefinitely. An IBM PC disk holds approximately 360k worth of
information (250 double-spaced pages of text). This is called a
Double-sided, Double-density Diskette. Newer, smaller 3.5 inch disk
exist which hold at least twice as much - 720k.
FIXED DISK DRIVE: Usually named disk drive C. It is essentially a
very large floppy disk. This Fixed Disk (commonly called a Hard Drive)
is secured within the machine and cannot be seen or transported. The
storage capacity is so large it is measured in megabytes (1M = 1K
squared = 1,048,576 bytes). Fixed Disks are available from 5M on up.
The advantage is that it is enough space to meet most users' total
storage needs, operates much faster than a floppy (5-10x faster), and is less
likely to fail since it lives within the protected computer.
KEYBOARD: Input device that lets you enter data into the
computer. The layout is similar to the standard QWERTY
typewriter keyboard, however there are many extra special
keys that are defined by the software you are running.
MONITOR: A television-like device that the computer uses to
communicate with you. Typically the monitor displays 80
columns (characters) by 25 rows (lines) of information.
PRINTER: Most users get at least one Printer for their
computer. It produces a "Hard-Copy" output of your data
rather than just being able to view it on the monitor. Dot-
Matrix printers are inexpensive and fast and can draw
graphics. Letter-Quality printers are more expensive and
slower but create pages better than typewritten (even
pressure on each keystroke).
MODEM: Short for Modulator/Demodulator. A device to send
and receive computer output over telephone lines.
ÚÄÄÄÄÄÄÄÄÄÄż ÚÄÄÄÄÄÄÄż
łKEYBOARD ł ÚÄÄÄÄÄż łMONITORł
łMouse ĂÄÄÄÄ INPUT ÄÄÄÄ>ł CPU ĂÄÄÄÄÄ OUTPUT ÄÄ>łPrinterł
łLight Pen ł ł RAM ł łPlotterł
łMicrophoneł ŔÄÄÂÄÄŮ łSpeakerł
łJoystick ł ł INPUT ŔÄÄÄÄÄÄÄŮ
ŔÄÄÄÄÄÄÄÄÄÄŮ ł and/or
ł OUTPUT
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄż
ł DISK STORAGE, Tape Storage, Modem, Fixed Disk Storage ł
ŔÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄŮ
DOS Level 1:
SOFTWARE: Sets of programs (stored sets of instructions) that govern
the operation of computer system and make the hardware run. These
programs (instructions) tell the hardware how to perform a particular
task such as word processing, games, database management, etc.
DOS
---
DOS - Disk Operating System - is a piece of software. However, it is
different from most software because a computer cannot run without it. It is
the first piece of software that is installed in RAM every time the computer
is turned on.
When the user first starts the computer, the DOS files must be available in
either the A drive or on a Hard Disk. The computer finds the desired DOS
files and automatically loads them into RAM. This process is often called
"BOOTING" the computer -from the computer pulling itself up by its BOOTstraps.
TO LOAD DOS
-----------
"Cold" Boot: Turning the computer on
"Warm" Boot: The computer has already been started, but you wish to
completely "clean-out" RAM and re-load DOS. This is a
much faster method of re-starting the computer since it
skips the usual system checks. To accomplish, you press
three keys simultaneously: <CTRL>-<ALT>-<DEL>
DOS performs 2 functions:
1. Links the Hardware
2. Allows for file management
We think of most software as enabling us to create something - like a document
or a spreadsheet. DOS's mission is vital. Firstly, it enables the hardware
devices to properly communicate with each other. It is a set of instructions
so that the computer's brain understands how its arms and legs operate
(keyboard, monitor, printers,...). We take this ability for granted. It is
like starting a car - many complex systems must work in unison for it to work,
yet we take it for granted that it will start.
The second function of DOS is also important. We must have a means to manage
the files that we save on our Floppy Disks or Hard Drives. There are times
when we wish to copy these files from one disk to another, or erase them, or
determine which files are on a disk. These tasks are performed often and the
software required to do so is DOS.
When DOS has been properly loaded from either a Floppy Disk or a Hard Drive,
the familiar "DOS Prompt" will appear. This prompt will look something
like this:
A>
This symbol signals 3 things:
1. DOS has been properly loaded into RAM
2. "A" is the DEFAULT drive
3. Awaits a DOS file management command
Each disk drive and hard disk has a letter associated with it. If a drive is
considered the DEFAULT drive, then the computer will always assume that the
information needed is in that drive, OR if something you have created is saved
- it will be saved to that drive, UNLESS you tell the computer otherwise.
All types of disks contain files. We use DOS as a software tool to manage
these files. We not only tell the computer which file we want to erase or
copy but also which drive it is currently in.
DOS FILE CONVENTIONS
--------------------
FILES: Any related set of instructions - programs, documents,
spreadsheets, etc.. A floppy disk is like a file cabinet with each
folder representing files on the disk (in the cabinet).
Rules: filename | extension (optional)
|
1-8 Characters | 1-3 Characters
No Spaces | No Spaces
Letters/Numbers| Letters/Numbers
If an optional extension is used, a period is used to separate the filename
and extension.
Many characters are allowed in filenaming. The following are INVALID
for filenames OR extensions:
. " / \ [ ] : | < > + = ; ,
Each file has a name. When you want DOS to act on a file, you must
specify its proper name (including its extension if applicable). A
file's name is made up of a filename and an optional extension:
saledata.jly
³ ³ ÀÄÄExtension (optional) - UP TO 3 CHARACTERS
³ ÀÄPeriod required as Separator IF extension used
ÀÄÄFilename - UP TO 8 CHARACTERS
Some filenames: SAMPLE
SAMPLE.DOC
BUDGET.WK1
Two files with the same exact name CANNOT exist on the same disk or
subdirectory (subdirectories are covered under hard disk sections).
FILESIZE
--------
Computers use 1 BYTE to represent 1 character such as a letter of the
alphabet, a number, a punctuation mark, a space, etc. A BYTE is also a unit
of measure since it represents 1 character. We measure the size of RAM in
Bytes, as well as the size of Files/Programs in Bytes.
We also measure the capacity of Disks and RAM in Bytes. So many Bytes
can be contained on disks or RAM that we talk about:
KILObytes = 1,000 bytes (often abbreviated "k")
MEGAbytes = 1,000,000 bytes (often abbreviated "meg")
5.25" disks Double Sided, Double Density = 360k
Double Sided, High Density = 1.2meg
3.5" disks Double Sided, Double Density = 720k
Double Sided, High Density = 1.4meg
Hard Drives = 10meg, 20meg, 30meg, 40meb, 60meg,......350meg
FREQUENTLY USED DOS COMMANDS
----------------------------
When DOS is booted, a copy of INTERNAL DOS commands are placed in the
computer's memory (RAM). These are called INTERNAL commands because
they stay in RAM until the computer is turned off. To use these
commands you do not have to re-insert the DOS diskette.
The rest of the commands on the DOS disk are called EXTERNAL commands
because they are NOT read into RAM when you boot DOS. Rather, to use them
DOS must accessible in one of the disk drives.
The following are some frequently used DOS commands:
INTERNAL ³ EXTERNAL (Insert DOS in Drive A)
³
DIR TYPE ³ FORMAT CHKDSK
COPY CLS ³ DISKCOPY
ERASE DATE ³ COMP
RENAME TIME ³ DISKCOMP
A>DIR B: - To find out what files are on a diskette in the specified
drive (B in this example). If just DIR is typed and entered,
a listing of files in the default drive (A in this case) will be
displayed.
A>DIR B:/P - Displays list of files one screen at a time
A>DIR B:/W - Displays list of files using the entire width of the screen
NOTE: The /P and /W options shown above for the DIR command are called
command switches. Most DOS commands have a variety of switches to alter
the core command.
A>COPY A:filename.ext B: - To copy one file from Disk A to Disk B
instead of an entire diskette.
A>DEL B:filename.ext - To remove the specified file(s) from the disk in
the specified drive.
A>DATE - To change the system date. This date will be "stamped" on each
file created or edited.
A>TIME - To change the system time.
A>CLS - To clear the screen
A>FORMAT B: - Prepares a new disk in Drive B for use on the IBM PC. If an
old disk is used, it will erase its contents. (Follow on-
screen directions)
A>FORMAT B:/S - Same as above, BUT ALSO Installs the INTERNAL DOS
commands on the new disk. Thus, this disk is now
capable of starting the machine.
A>CHKDSK B: - Indicates the number of files and amount of free storage
space remaining on the disk in drive B. It also indicates the
amount of RAM storage.
A>CHKDSK A: /F - Fix any problems that CHKDSK finds (converts lost clusters
to *.CHK files which can later be deleted)
A>DISKCOPY A: B: - Making an exact copy of the diskette in Drive A onto the
diskette in Drive B. (Follow on-screen directions)
Remember, if the computer is not told differently, it will assume the DEFAULT
drive:
A>COPY A:sample.wk1 B:
is the same as:
A>COPY sample.wk1 B:
The "A:" in the first example is redundant.
DOS Level 2:
We have seen that DOS's mission is one of file management. Every software
has a purpose and DOS's is for housekeeping of files. However, we also saw
that DOS is unique because we can't run the computer without it. We must
"boot" the system with the internal DOS files each time we start the computer.
Finally, most people don't realize that DOS is also the Swedish word for
toilet. Which DOS is more important in your life? Too obvious to comment.
WHEN A COMPUTER IS POWERED-UP
-----------------------------
What actually happens when the computer is started? First, a factory preset
set of instructions residing in ROM are activated. ROM stands for Read Only
Memory. This set of chips can send instructions TO RAM, but it cannot receive
them - thus cannot be altered. The unalterable set of ROM instructions
performs systems checks to make sure all critical hardware components are
hooked up properly and in the case of RAM - operating properly.
Once the hardware check is performed, ROM instructs RAM to search the A drive
for internal DOS files. If no disk is present in drive A, then ROM directs
RAM to check the Root directory of the hard drive for the necessary files
(more on Root directories in Hard Disk DOS lessons). If the files are found,
they are automatically loaded into to RAM (booted).
There are 3 files which comprise internal DOS: IBMDOS.SYS, IBMBIO.SYS and
COMMAND.COM. The first 2 files are hidden files. They cannot be seen in a
DIR command, nor can they be copied or deleted with conventional DOS commands.
These files are responsible for the linking of the hardware components. The
final file, COMMAND.COM CAN be seen, copied or deleted, and contains the
frequently used internal DOS file management commands. Again, the system will
not boot without these 3 files.
It is from the DOS prompt: A>
that we can go forward with
the task of file management.
We have already seen a handful of the most useful DOS file management
commands. Lets expand their abilities with the use of file WILDCARDS.
WILDCARDS
---------
Wildcards allow the power of a DOS command to expand. For example, imagine
that you need to copy 12 files from a disk containing 100. The 10 files all
begin with the word SALES. Sales.Jan, Sales.Feb, Sales.Mar ...
We could copy each file individually: A>Copy Sales.Jan B:
A>Copy Sales.Feb B:
......
Or, we could do it in one command with the use of a wildcard:
A>Copy Sales.* B:
The asterisk (*) represents a wildcard. It is often referred to as a star.
The above command would read "Copy Sales dot star space B full colon".
Any DOS command that references a filename can make use of wildcards to
expand the command. When a Copy command is issued, DOS is instructed which
single file to copy. However, when we use a wildcard, DOS is instructed to
use any files that meet the criteria. The asterisk expands the criteria for
qualifying files.
A>Copy Sales.* B: says "copy any file from drive A to drive B that contains
SALES as the filename, regardless of the extension"
What if we wanted to include the files: SALES1.DOC, SALES10.DOC and
SALESMAN.SUM
SALES.* is not broad enough criteria to include these files. Rather, we would
state it:
A>Copy SALES*.* B:
Now the criteria is to copy ANY file as long as the first 5 characters are S A
L E S regardless of what other characters come after these first 5 in the
filename or what exists in the extension.
The asterisk is the broadest and most often used wildcard. Some other
examples of its use:
A>Copy *.DOC B: (all files with the extension DOC)
A>Del S*.* (any file that begins with the letter S)
A>Del B:*.* (ALL files from the B drive - be careful!)
A>Dir B:*.COM (A list of all files with an extension of COM
on the B drive)
Anywhere a file specification can be given in DOS, the specification can be
broadened with a wildcard. The asterisk is very useful.
Another wildcard is the question mark (?). It too broadens the criteria for a
command, however, it is "location specific". For example:
A>Copy S?.DOC B:
Any file that has S as the first character followed by a single character
in the second position or not, but NO more characters in the filename plus an
extension of DOC.
Therefore, these files would make it: S.DOC SA.DOC SI.DOC S5.DOC.
And, these files would not: SALES.DOC SAT.DOC S5.EXE
Wildcards can be used together:
A>Copy S?L*.* B:
This will use the following: SALES.COM SAL S5L.DOC SL.EXE
But not: SAM.DOC BUDGET.SL
The wildcard characters, * and ? are used with DOS commands such as DIR,
COPY and DEL to broaden their application. An asterisk, or "star" allows up
to 8 characters at any position in a file name. A question mark does the
same, but for only 1 character position.
DOS Level 3:
The world of DOS is a large one. There are many, many commands with optional
switches in the realm of file management. Fortunately, like most software
there is a flow and feel to DOS. After you are familiar with the core
commands, looking up additional ones and figuring out how to use them becomes
easier. The pattern is a DOS word (DIR, COPY, DEL....) followed by the
necessary, minimum information to make it go. For example:
A>DIR B: DIR only needs the drive the directory is
desired
A>Copy C:sample.doc B: COPY needs 3 pieces of information - what file
on which drive is to be copied to which drive
A>DEL B:Test.EXE DEL needs 2 pieces of information - what file
on which drive to delete
SOFTWARE VERSIONS
-----------------
Software is labeled with a version number. With each subsequent release of
the product, the version number increases. The reason for these upgrades are
to rid "bugs" (problems) within the software, significant product
improvements, and/or to exploit new hardware advancements. In general,
anything created on an earlier version of a software will work with a later
version of the same software. This is known as upward compatibility. The
reverse is rarely true.
DOS first hit the market as version 1.0 in 1981. It has gone thru many
upgrades as new hardware components became available and new DOS features were
added. Currently DOS 4.X is available. However, most systems are still
using DOS 3.X versions. For a single user system, any DOS version over 2.1
is probably adequate. If you are using high density 3.5 inch floppy
drives, you will need at least DOS 3.X.
When application software is purchased, DOS version requirements are noted on
the package as well as RAM requirements.
FILE ALLOCATION TABLE
---------------------
As was discussed earlier formatting a new floppy disk prior to use,
electronically superimposes a grid system on the disk. Each grid intersection
(sector) is numbered. The location of files pieces on a disk are noted in a
File Allocation Table (FAT) on each disk. When a file is copied to a disk,
the FAT is checked for available sector locations.
The FAT is like an index to the location of file pieces on the disk. File
portions DO NOT have to be in adjacent sectors. As a disk repeatedly has new
files copied to it and old files deleted, files become fragmented - portions
of the file exist in non-adjacent sectors. This situation is referred to
as non-contiguous sectors. Data integrity is not affected by this situation,
but the speed in which data can be retrieved is. There are many third party
products to "defragment" a disk. If the programs you will be using are disk
intensive - like accounting or database management, you will notice a slowing
of program execution over time as files become fragmented.
When a file is deleted from a disk, the contents are not wiped from the
sectors, rather the file name is removed from the FAT and the associated
sectors are now simply declared available for new data. This is important to
understand because deleted files are actually still on the disk but their
locations are now not considered off limits. Again, many third party software
products are available to undelete these files.
If you do delete a file, try not to use the disk until the proper utility
software is available to reverse the deletion. With more use, you are running
the risk that the next file that is copied to the disk will occupy the
sectors of file you wish to undelete. If that should happen, you will not be
able to undelete the "old" file.
Some popular third party utility tools to defragment a disk and allow
undeletion include PC TOOLS, NORTON UTILITIES, MACE UTILITIES, VOPT DISK
OPTIMIZER.
BATCH FILES
-----------
Batch files are a DOS tool that allow you to automatically execute 1 or more
DOS commands sequentially. A more detailed explanation can be found under
Hard Disk Dos sections.
For example, you are tired of changing default drives, subdirectories and
typing the word LOTUS each time you wish to enter into the LOTUS 123
spreadsheet program. The 3 steps required are:
A>C:
C>cd\lotus
C>lotus
These steps can be combined with a single BATCH file called LOT.BAT.
To build:
C>copy con:lot.bat --- Begin creating a file called lot.bat
C:
cd\lotus
lotus
<F6> --- End building and save to disk by
pressing the <F6> function key
Now, each time LOT is entered at the DOS prompt, the commands within the
LOT.BAT file are automatically executed sequentially.
C>lot
REDIRECTION
-----------
Redirection refers to having input or output come or go to devices other than
the standards of Keyboard (Input) and Monitor (output). In DOS we expect to
enter commands from the Keyboard and have the results displayed on the
Monitor.
A>DIR --- Gives a directory of the A drive disk on the
monitor
A>DIR >PRN --- PRN means to send the results of this command
to the printer
A>DIR >LIST.TXT --- Now the output of this command is put into a
file on the A disk called LIST.TXT (any
filename could have been used)
The greater than sign ( > ) used above was to REDIRECT the output to a
Printer and a Disk File rather than the default output device; the monitor.
This is useful for getting a hard copy print-out of a particular disk's
contents.
PIPING - FILTERS
----------------
Piping is a way of telling DOS to transfer the output from one command to be
the input for another command. Piping is a form of redirection except DOS
will create a temporary file on a disk to accomplish the task.
Piping usually involves the use of special commands, termed Filters, to accept
data, do something with it, and then pass it to the next step. There are 3
standard filters used by DOS in piping:
FIND - used to search a file directory for a specified string of text
MORE - used to display one 1 screen of output at a time
SORT - used to sort disk filenames
The symbol used by DOS to indicate a Piping operation is the vertical bar (|).
Examples:
A>DIR |sort --- Will display on the monitor the list of files
on the A disk, BUT in filename alphabetic order.
A>DIR |sort/+10 --- Will display on the monitor the list of files
on the A disk, BUT by alphabetic order of the
filename extensions. Extensions are 10
characters from the left on the screen during a
DIR.
A>DIR |sort >prn -- Same as the 1st example except the results of
this command will be printed out.
A>DIR |sort >SAM.D - Same as the 1st example except the results of
this command will be saved in a file on the disk
called SAM.D
A>DIR |sort |more -- Will display in sorted order one screen at a time
A>DIR |find "05-14-89" -- Will display a list of files that were last
changed on May 14, 1989
A>DIR |find "SALES" -- Will display a list of files that have the
word SALES in the file name
Hard Disk Management - Level 1:
DOS Disk Operating System (Director Of Services)
---
Master control program for the flow of information within a PC. One of
its primary functions is to oversee all disk activities -
reading/writing information from/to a disk, and loading/executing
programs. It controls (links) all hardware devices so they may
communicate with one another including:
Floppy Drives: 5.25", 3.5"
Hard Drives: 10mb, 20mb, .....
Ram Disk: Simulates a disk drive from within RAM
Laser Disk: "CD's" for computers
Tape Storage Device: Backup system typically using cassette type
tapes
PLUS, Screen, Keyboard, Printer, Modem, Mouse, ...
As if this wasn't enough, this modest software called DOS also keeps
track of the current time and date, and the usage of all memory
locations within RAM.
Once DOS has been properly BOOTed, you will see the familiar "DOS
Prompt":
A>
This says: 1. DOS has been properly installed
2. "A" is the default drive
3. DOS is awaiting your next command
HARD DISK DRIVES
----------------
Also called Hard Drive, Hard Cards, Fixed Disk Drives. Hard Drives are
essentially large floppies housed within the computer. They are much faster,
much higher capacity, and less likely to fail due to the safe environment from
within which they operate.
Hard Disk cost is related to its capacity and it Access Time. Access Time is
the amount of time it take the disk to locate a random piece of information.
Access Time is measured in milliseconds (ms-millionths of a second). A fast
one would be 28ms, a slow one 65ms.
DOS REALITIES
-------------
There are three types of FILES that may be successfully "executed" from
the DOS Prompt:
1. *.EXE Commands ("EXECUTE" Program files Lotus, dBASE,....)
2. *.COM Commands ("COMMAND" Program files Lotus, dBASE,....)
3. *.BAT ("BATCH" Custom programs )
To successfully execute one of the *.EXE, *.COM, or *.BAT command
files, the file itself must be either:
1. In the Current directory
2. Within a directory that is part of the DOS "PATH" command
Batch (.BAT) files are the only executable files you can write using a
simple word processor, or DOS's built in Line Editor (EDLIN) - more later.
BOOTING (or Bootstrap) To load and execute the Disk Operating System-DOS
-------
This term comes from the phrase "pull yourself up by your own bootstraps".
This happens within a PC when it is turned on. Actually, a built-in program
(ROM) is executed, then a couple of "hidden" files from the ROOT directory
(hard drive) or DOS Disk (floppy disk), then COMMAND.COM (DOS internal command
interpreter) followed by the Optional CONFIG.SYS and AUTOEXEC.BAT files.
COMMAND.COM: Must by loaded for DOS to operate properly, it contains
the Internal DOS commands - those used most often: Copy,
Dir, Del, etc. The remainder of files on the DOS disk
are called External Files (DISKCOPY, CHKDSK,...). To
utilized one of these commands, the DOS disk must be
accessible.
CONFIG.SYS: Optional. If it is located on the Disk that you are
BOOTing from, DOS will "open" it and read and interpret a
list of system configuration commands. This is a ASCII
text file which can be created by any text editor.
Configuration commands include: FILES, BUFFERS,
DEVICE,...
AUTOEXEC.BAT: Optional. An ASCII text file. "Opened" and read after
CONFIG.SYS, IF it exists on the BOOT disk. A "batch"
file. A set of DOS commands and other special commands.
SOME FREQUENTLY USED DOS COMMANDS WITHIN A HARD DISK ENVIRONMENT
----------------------------------------------------------------
A Hard Disk is just like a floppy. However, due to its size additional file
management commands are needed. The following can also be used on floppy
disks, but they are most common in Hard Drive Environments.
INTERNAL і EXTERNAL (Insert DOS in Drive A)
і
MD і CHKDSK
CD і BACKUP
RD і RESTORE
PROMPT і SUBST
PATH і TREE
MD - Make a directory (see below)
CD - Change to a directory (see below)
RD - Remove a directory - must be rid of files first (see below)
PROMPT $p$g - Changes the way the DOS prompt is display. $p$g insures that
the current directory is shown at the prompt. Very useful.
Usually "set" in the AUTOEXEC.bat file (see below)
PATH=c:\DOS;c:\BATCH;c:\UTILITY
Sets up a command (*.EXE, *.COM, *.BAT) search path in the DOS
environment. When a command is issued from the DOS prompt, it
first looks in the directory you are currently in, then looks in
each directory noted on this path. Usually this command is built
into the AUTOEXEC.bat file (see below)
CHKDSK C:\*.* /F
Checks the integrity of disk files - the level of fragmentation of files.
Indicates the number of files and amount of free storage space remaining on
the disk in drive A. It also indicates the amount of RAM storage.
If any lost clusters are found (data without a home), they can be converted
to *.CHK files so you can delete them to free up the disk space.
SUBST E: c:\LOTUS\123FILES - Assigns a 1-letter drive ID to a
directory path
SUBST E: /D - Cancel previous designation
TREE /F - Displays a list of files and directories on the disk.
/F - more detail - all files, all directories
BACKUP (see below)
RESTORE (see below)
DIRECTORIES
-----------
As previous mentioned, a hard disk is essentially a large floppy disk.
However, it offers some distinct advantages:
Is much larger
Stays inside the machine
Operates (transfers data) at a much higher rate (5-10x)
Because a Hard Disk is so much larger than a floppy, we use an
additional file organization tool called SUBDIRECTORIES.
If a floppy is like a filing drawer, than a Hard Drive is like a wall
of file drawers, each drawer call a SUBDIRECTORY.
DOS lets you organize files using tree-structured directories rather than a
single directory. In other words, since a 20 meg (20,000,000 byte) capacity
hard drive can contain approximately 60 floppy disks worth of files, an
additional organization tool is needed. The creation of SUBDIRECTORIES allows
us to subdivide a disk to contain related files. It's as if we have many file
cabinets available to store our files rather than a single giant one.
DOS permits up to 112 files on a floppy disk. However, with that many
it is a labor to examine via a DIR and it also slows DOS's file access
and retrieval.
ROOT DIRECTORY - Main directory - it provides support for all the
SUBDIRECTORIES. It contains all the SUBDIRECTORIES.
Each SUBDIRECTORY can contain files as well as other SUBDIRECTORIES.
These other Subdirectories could be thought of as SUB-SUBDIRECTORIES.
To use a file in a different drive we have specified the drive and
filename (B:Filename.ext). Similarly, if we want to access a file in a
SUBDIRECTORY we specify a PATH, OR make that SUBDIRECTORY the "current"
one.
ЪДДДДДДДДДДДДДДї
іROOT DIRECTORYі
і і
і filesі
АДДДДДДВДДДДДДДЩ
і
ЪДДДДДДДДДДДДДДДДДДДДЕДДДДДДДДДДДДДДДДДДДДї
і і і
ЪДДДДДДБДДДДДДДї ЪДДДДДДБДДДДДДДї ЪДДДДДДБДДДДДДДї
іSUBDIRECTORY і іSUBDIRECTORY і іSUBDIRECTORY і
і filesі і filesі і filesі
АДДДДДДДДВДДДДДЩ АДДДДДДДДДДДДДДЩ АДДДДДДВДДДДДДДЩ
і і
ЪДДДДДБДДДДДДДДДДДДДДДДДДї і
ЪДДДДДДБДДДДДДДДДДДї ЪДДДДДДДДДБДДДДДДДДї ЪДДДДДДБДДДДДДДДДДДї
і"SUB-SUBDIRECTORY"і і"SUB-SUBDIRECTORY"і і"SUB-SUBDIRECTORY"і
і filesі і filesі і filesі
АДДДДДДДДДДДДДДДДДДЩ АДДДДДДДДДДДДДДДДДДЩ АДДДДДДДДДДДДДДДДДДЩ
PATH: A PATH specifies the names of the directories that DOS must go
through from the ROOT DIRECTORY to get to the file. The directories
are separated by a forward slash ( \ ). (NOT the same as the DOS PATH
command noted above)
EX: C:\123FILES\PROJECTX\BUDGET.WK1
C:\ Root Directory
і
ГД 123FILES Lotus files Subdirectory
і
АДДВДД PROJECTX Sub-Subdirectory containing all "PROJECTX"
і files
і
АДДДДД BUDGET.WK1 A specific Lotus file called BUDGET within
the PROJECTX Subdirectory
DOS & SUBDIRECTORIES - there are only 3 key commands in dealing with
Subdirectories: MD, CD, and RD
TO MAKE A SUBDIRECTORY
----------------------
MD dirspec - Internal - to MaKe a DIRectory -dirspec is the name of
the subdirectory or its PATH
EX: C>MD 123FILES <ENTER> - This creates a subdirectory
called 123FILES
- Naming a SUBDIRECTORY follows the same rules for
file naming, except extensions are not used
- You can created unlimited number of SUBDIRECTORIES
- Identical Filenames can exist in different SUBs
(Remember, 2 files with identical filenames CANNOT coexist
in the same SUBDIRECTORY)
TO CHANGE THE "CURRENT" SUBDIRECTORY
------------------------------------
The computer can only have 1 "file drawer" open at a time - thus this is
called the current directory. Unless instructed otherwise, the computer will
assume all files sought and sent will go into this current subdirectory.
CD\dirspec - to Change the "current" Directory
- EX: C>CD\LOTUS <ENTER> - This makes a subdirectory
called LOTUS the current one
TO REMOVE/ERASE A SUBDIRECTORY
------------------------------
1. First make this directory the current one C>cd/dirspec
2. DELETE all the files within this directory
C>DEL *.*
It will ask if you are sure - Y
3. Go to the ROOT DIRECTORY C>cd\
4. RD dirspec - Reove Directory
C>RD dirspec
Hard Disk Management: Level 2
BATCH FILES
-----------
These are user created files that have the extension .BAT
The file itself contains lines of DOS commands. Some think of these
files as "macros". They can be created with an ASCII text editor
including the built in EDLIN editor (see below), or can be created from "the
console" (keyboard) via COPY CON.
These are very useful for program startups.
Use the TYPE command to view the contents of a batch file:
C:\>TYPE 123.BAT
c:\
cd\lotus
123
cd\
cls
Use the PRINT command to print out the contents of a batch file:
C:\>PRINT AUTOEXEC.BAT
The PRINT command is like the TYPE command except it is an external DOS
command and send output to the printer instead of the screen. Another
approach using redirection discussed earlier would be:
C:\>TYPE AUTOEXEC.BAT >PRN
AUTOEXEC.BAT
------------
This user created, optional batch file is sought out by DOS when the
system is BOOTed. If this file is on the BOOT disk, DOS will
AUTOmatically open it and EXECute it.
This is outstanding way to automate the execution of certain DOS
commands like DATE, TIME, PATH, PROMPT, etc - which should be done
EVERY time the system is booted.
EX:
date
time
path c:\;c:\dos;c:\batch;c:\utility
subst e: c:\dbase\dbfiles
prompt $p$g
cls
CONFIG.SYS
----------
This too is an ASCII file created and viewed like AUTOEXEC.bat. It
also is optional and is sought out by DOS when the system is BOOTed. HOWEVER,
the command lines that this file uses ARE NOT DOS type commands found in .BAT
files. Rather, these are special CONFIGuration SYStem commands.
CONFIGuration SYStem commands are needed to define certain hardware
parameters. For example, if your system uses special size disk drives,
extra printers, extra modems, extra input devices (joysticks, mouse),
RAM disks, etc.
EX: CONFIG.sys
FILES = 20
BUFFERS = 15
In this example, FILES = 20 means that DOS will allow up to 20 files opened
simultaneously. If this line were not present in CONFIG.SYS, DOS would only
allow up to 7 files. Do we need up to 20? Certain programs (dBASE,
Accounting, etc) state early in their manuals that this parameter needs to be
set at 20 for the software to operate correctly.
The BUFFERS = 15 defines a staging area within RAM for portions of files that
are not on the screen yet. For example, in an Accounting program if you told
the computer to bring up the last 10 invoices entered, it would display these
10 invoices. However, unknown to you it actually took the last 30 invoices in
anticipation that you would want to see them right away also. The extra 20
that the system brought into RAM are sitting within the BUFFERS. DOS allows
this and does this as a way to speed up the system. Items that are sitting in
RAM can be accessed seemingly instantly versus items that must be sought from
a disk.
If not told, DOS automatically sets BUFFERS to 3. If BUFFERS are so useful,
why not set them to their maximum of 99? The reason is that DOS is guessing
which information you will need next. If it guesses wrong - for example the
next invoice you wish to look at is 1500 ago, it must first check all the
BUFFERS before realizing that it will have to go to the disk to retrieve the
needed information. It actually slows the process down in this case. Most
purchased software will note if this command is needed and what to set it to.
BUFFERS = 15 is a common level to operate at.
EDLIN
-----
Edlin is a LINe EDitor supplied with the DOS disks. It is a very basic word
processor that allows the creation and editing of Batch Files including
AUTOEXEC.BAT and the CONFIG.SYS file. These files are like documents that the
computer reads and interprets. Each line of these files contains a single
thought for the computer. EDLIN is a device to create these documents.
To enter the EDLIN environment you type the word EDLIN followed by the name of
the file you wish to create or edit:
C:\>EDLIN CONFIG.SYS
An asterisk will appear:
*
You will type the letter I and press enter to go into the Insert mode:
*I
The computer responds with:
1:*
This 1 refers to line 1 of the CONFIG.SYS you are now creating. You will now
just type each line and press enter. When finished you will press the <F6>
key to return to the furthest left asterisk:
1:*FILES = 20
2:*BUFFERS = 15
3:<F6>
*
At this asterisk you will now type E and press enter to End the process and
save what you just created:
*E
C:\>
Other EDLIN commands from the left most asterisk:
*L - this would List on the screen the entire contents of the
file being edited
*3D - this would delete line #3 from the file
*4I - this would allow inserting a new command beginning at line #4
*5 - this would allow making changes to line #5
EDLIN is adequate for creating and editing small Batch type files. We saw
earlier that there is another technique for creating these files utilizing the
COPY CON command. It is even more limited than EDLIN.
BACKUP and RESTORE
------------------
Periodically the entire hard drive or at least the subdirectories
containing data files should be BACKed-UP onto floppies or tape for
safe storage in the event of a hard drive crash or accidental erasure.
Should that happen, the files are then simply RESTOREd.
DOS provides two commands to accomplish this - BACKUP and RESTORE
commands. Unfortunately, these are slow and problematic. The world is
full of third party alternatives that are far superior in speed, ease
of use, data compression, and ability to incorporate into batch files
so the operator only need to "kick-off" a batch file and have a supply
of floppies nearby to complete.
EX: Using DOS commands:
C:\>BACKUP C:\lotus\*.wks A: /S /M
"A" is the DESTINATION drive
C:\lotus is the SOURCE directory
*.wks specifies any files with an extension .wks (worksheet files)
/S specifies any Subdirectories beneath \LOTUS directory
(that contain *.wks files)
/M only the files that have been Modified since Last BACKUP (using the
same disk set as last used during the BACKUP)
NOTE: Have a supply of disks for the "A" drive ready. These floppies do not
have to be formatted. If more than 1 is required, be sure to number in
sequence. This process will erase whatever used to be on the disk.
Now, if the files need to be restored to the hard drive due to failure
or erasure: Start out with "disk #1" in the "A" drive.
A:\>RESTORE A: C:\lotus\*.wks /S /M
"A" is now the SOURCE
/M only files Modified or Deleted since they were backed up
These commands were designed for emergency situations. It is better than
nothing. Many wish to use them as a way to transfer a large group of files
from one machine to another. This will only work if the version of DOS on
each machine is identical.
Another problem is that you end up with a very large number of disks. There
is no data compression (which most competing products provide) which results
in up to 50% fewer backup disks.
A final hazard: If you end up with 20 disks, and disk number 10 is lost or
destroyed, you may never be able to access disks 11-20 or 1-9. The 20 disk
set is like one continuous floppy disk. By destroying 1 disk, it is like you
destroyed the giant continuous floppy. This is not true of competing products
like FASTBACK, PCTOOLS or NORTON UTILITIES.
XCOPY
-----
Beginning with DOS 3.2, the XCOPY command is a useful hybrid of the COPY
command and the BACKUP/RESTORE mess. It addresses the issue that COPY cannot
copy more files than a disk can hold. But, XCOPY cannot copy a single file
that is larger than a single disk like the BACKUP command can.
C:\>XCOPY C:\*.* a: /S /M /D:mm-dd-yy
The options: /S - includes all subdirectories hung from the current one
(in the case shown we are in the root directory)
/M - includes only files that have been modified since the
last XCOPY was performed
/D:mm-dd-yy - include only files with a date greater or
equal to the one specified
XCOPY is: - Faster than the COPY or BACKUP commands
- Able to transfer entire directories like BACKUP can
- Copy files selectively by modification status or date
- Able to use the COPY command (which is DOS version independent)
to copy individual files at a later date - unlike BACKUP
- Unable to copy single files that are larger than a single disk
(BACKUP is able to do this - remember the 1 continuous disk
concept)
- Target disks must be formatted
HARD DISK ORGANIZATION PRINCIPALS
---------------------------------
1. Put only directories in the Root directory except;
Command.com, Config.sys, Autoexec.bat
2. Use many batch files. Put them in a \BATCH subdirectory
3. Keep the PATH command short in autoexec.bat
PATH = c:\DOS;c:\BATCH;c:\UTILITY
4. Keep the directories sorted (use third party software tools)
5. Defragment files on a regular basis - use some third party
software; PC-TOOLS, NORTON UTILITIES, VOPT, etc