HOW DOES A COMPUTER WORK

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HOW DOES A COMPUTER WORK??

• This presentation will help you to understand and
  remember the basic workings of a computer.

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A computer is like an office. The two major
fixtures
File cabinet
Desk
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The File Cabinet in the Office...
The Hard Disk in the Computer...

• Stores work not currently being used
• Size is measured in number of drawers
• More drawers means more storage
• But increasing drawers does not speed things up

• Stores files data and programs not currently in
  use
• Size is measure in bytes
• 540 mb, 1.2 gb, 4 gb
• Larger disk means more storage, but no more speed
  

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The Desk Top in the Office
Main Memory in the Computer...

• RAM Random Access Memory
• All files in use are here
• Measured in bytes
• 640 kb, 4 mb, 16 mb
• More RAM
• More files in use at once
• Faster operation

• Everything currently in use is here
• Is measured in square inches
• Larger desk means more files may be in use

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But..who does all the work???

• Not the desk.
• It is just the place where work is done.
• Not the file cabinet.
• It is just the place where work is stored.
• The work is done
• by a PERSON.

The Person is the CPU--the Central Processing Unit
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The person who does all the work...

• Can follow instructions
• This is the control function
• The control unit in the CPU executes instructions
• Has a pocket calculator
• This is the arithmetic capability
• The A/LU arithmetic/logic unit in the CPU

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The person in the office represents the CPU--the
Central Processing Unit
The CPU is a chip--tiny circuits photographically
printed
Intel

• The CPU has two major functions
• The Control Unit Control executes instructions
• The Arithmetic-Logic Unit A/LU performs
  arithmetic operations

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Important characteristics of the CPU

• POWER
• In general, the more things the CPU can do with a
  single instruction, the more powerful it will be.
• So, bigger chips mean more power.
• SPEED
• The faster the CPU operates, the more it will do
  in a given time period.

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The person in the office /the Central Processing
Unit

• The capability of the person
• power of the processor
• 486 Pentium
• The speed of the person
• clock speed of CPU
• 200 mhrz. 166 mhrz.

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• Lets select someone else.

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Typical CPUs

• Intel 386
• Intel 486
• Intel Pentium
• Intel Pentium MMX
• Intel Pentium II
• Cyrix

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Now lets put these three things together..

• 1. The person is the Central Processing
  Unit--the CPU. This person does the thinking.
• 2. The top of the desk is Main Memory--RAM.
  This is the work place.
• 3. The file cabinet is the Hard Disk Drive.
  This is the place where all work is stored.

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The desk in the office...

• All work must be laid out on the desk top
• The person in the office can work on nothing else
• Sothe size of the desktop determines how much
  work is immediately available
• More square inches, more work accessible
• A job may be too large for a small desk

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The size of RAM...

• The CPU may use only what is copied into main
  memory RAM--so RAM must be large enough
• RAM is measured in Bytes
• one byte is enough space to hold one letter
• Typical sizes of RAM
• 640 Kb 640,000 bytes a long time ago!
• 1 meg. 1,000,000 bytes
• Current sizes 8, 16, or 32 mb.

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The file cabinet represents the hard disk drive.

• The HD stores two kinds of files
• data
• programs software
• A magnetic surface on the disk permits recording,
  like cassette tape.
• Typical sizes
• 540 mb now out of date!
• 1 gig. 1,000,000,000 bytes
• 2 gig., 4 gig. are typical

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Everything is stored in the filing cabinet

• Sets of instructions descriptions of how to
  process data are stored there ready to be used.
• Data the information to be used by a set of
  instructions are stored there.
• Anything in the file cabinet must be moved
  actually copied to the desk top to be used.

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The desktop and file cabinet--RAM and the HD

• Files are copied from HD to RAM
• CPU has access only to what is copied into RAM

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A REVIEW TO THIS POINTThe most important
matters about a computer.

• Which CPU does it have?
• How many bytes of RAM main memory does it have?
• How large is the HARD DISK where data and
  programs can be stored?

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BIG PROBLEM.. the office is a closed room. How
can the outside world communicate?

• What do we use in a real office?
• Telephone talks to other offices
• Typewriter prints things to send out
• Intercom system brings messages in

So a computer needs Input/Output Units -- I/O
Units
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To compare the office and the computers I/O

• The typewriter sends data out of the office
• and represents the printer.
• The intercom receives data into the office
• and represents the keyboard and mouse.
• The phone sends and receives to other offices
• and represents the modem.
• Disk drives may be considered as auxiliary
  storage of as combination input/output units.

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What are other I/O Units?

• Input units
• The keyboard
• The mouse
• A modem
• CD-ROM drives
• Bar-code reader
• A scanner
• Disk drives

• Output units
• The monitor
• Printers
• Speakers
• Robots
• Disk drives

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Nowthe computer in operation

• Man very smart, can do anything, but has not been
  told to do anything. He stares at empty desk.
  Nothing happens.
• There must be some first built-in instructions.

• Computer all ready
• man at desk
• calculator in pocket
• file cabinet ready
• We turn the light on computer is powered up

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The need for ROM...

• In addition to RAM a blank place to write
  things, a computer must have a place where a few
  built-in instructions always reside. This place
  is called ROM--Read Only Memory--memory that
  cant be erased.
• So, on the desk top are a few permanently written
  instructions.
• Actually these instructions are permanently
  written, or burned, in a chip

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Again, a computer in operation..
Man at desk. The light is turned on. He looks
down and sees written on the desk top 1. Check
the desk top to see that it is ready. 2. If it
is, open the first drawer of the file cabinet and
remove the first folder. Spread papers on the
desk. 3. Read instructions and follow
them. What the instructions from the file cabinet
include How to use the typewriter, phone, and
other devices Wait for further instructions.
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What just happened in computer terms...

• The computer was turned on.
• The CPU following instructions in ROM checked
  memory and certain other things in the
  computer.
• The Operating System OS was copied from HD to
  RAM.
• All drivers needed were loaded.
• The CPU awaits user instructions.

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What is multitasking?

• One program is running. You move it to the
  background and load another.
• Now two programs are on the desktop but only
  one appears on the screen. Both are running.
• Sufficient RAM is needed for multitasking.
• You may move from one application to another
  without having to reload it.

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What is a driver for a printer?

• Suppose the entire OS were in ROM
• Code to driver printer would be in ROM
• When a new printer is purchased, the old OS could
  not drive it.
• But, OS is on HD and copied into RAM along with
  drivers
• With new printer, a new driver copied to HD. Now
  OS loads new driver.

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What will more RAM do?

• Too little RAM will prevent programs from
  running.
• More RAM will let more programs run at
  once--multitasking.
• More RAM will let programs run without having to
  run the HD for temporary storage.
• So, some programs will run faster.
• Once you have enough RAM, adding more will not
  speed things up.

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What will a larger HD do?

• Too little HD space will prevent saving files you
  are working on.
• Too little space will prevent loading new
  programs.
• A larger hard disk will permit storing of more
  data and programs.
• Otherwise, more disk space will not speed up
  computer operations.

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A problem..

• The file cabinet holds many files.
• But what if you want to carry a file to another
  office?
• You cant take the whole file cabinet very
  easily.
• So, you need...

A smaller, but portable, file carrier
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And that is...

• A diskette or floppy disk
• Diskettes hold less than the HD
• 3? diskette 1.44 meg.
• But are portable

Diskettes are Brief Cases for the computer.
Diskettes are used ...to take files to other
computers to load new software to make
backups for safe keeping
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Typical specs for a PC...

• Processor
• Memory
• Hard Drive
• Modem
• Video RAM
• Sound card
• CD-ROM drive
• Diskette drive

• Pentium II
• 8, 16, 32 meg.
• 1, 2, 4 gig.
• 56 kbps
• 2 meg.
• Soundblaster
• 24x
• 1.44 meg., 3?

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Nowyou know what is inside a computer and how it
works!!

• Its really very simple. Isnt it?

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You are now a certified computer whiz!!
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