Computer Chips:

Computer Chips are constructed out of silicon which is a semi conductor.  A semi conductor does not allow electrons to flow through the semi conductor but does allow the storage of electrons in the semi conductor and retrieval of the information by drawing circuits on the surface of the silicon. This is possible with Silicon because of the its atomic structure.  http://periodic.lanl.gov/14.shtml. This link discusses the history and properties of Silicon.

ROM - Read Only Memory Chips

The first computer chips developed were called Read Only Memory - ROM.  These chips came with an instruction set (program) when purchased.    When the computer is turned on the data is transferred in to main memory.  When the computer is turned off the data remains in the chip.  The data can not be modified on the chip. 

PROM - Programmable Read Only Memory Chips

 Industry, like the car makers and others, told the chip builders that they wanted a chip that could be developed for specific purposes. The Programmable ROM chip was developed.  This chip had a glass window on the top that allowed a laser beam to program the chip once after it was built.  This way industry could get a chip to plug into their computer for a specific job.

EPROM - Erasable Programmable Read Only Memory Chips

Industry after a while said to the manufactures of chips "we don't want to continue buying a new chip each time we change our program how about a chip that can be erased and reprogrammed." The outcome of this request was the Erasable Prom.  EPROM chips also had a glass window by which a laser beam could program the chip, erase the program, and reprogram it many times. Industry still had to send the chip back to the company for the erasing and reprogramming. 

EEROM - Electronically Erasable Read Only Memory Chips

Industry then said "we don't like having to pay you all of the time to erase and reprogram our chip, especially when it takes so long".  In 1991 Sycor and MIT developed the Electronically Erasable ROM chip.  EEROM technology currently replaces disk drives and cd drives in the 2001 digital cameras. Often it is referred to as Flash Memory, Stick Memory, USB Memory, Chip Memory, and etc. When power is on the chip can be programmed.  When power is turned off the data remains in the chip.  Power can be put back on, the data transferred and the chip can be electronically erased. Eventually EEROM chips will replace HD, FD, and CD's on our PC's and Digital Cameras. 

RAM - Random Access Memory Chips

Random Access Memory chips are fully addressable.  Each and every byte of data is stored at a specific hexadecimal address in the chip and can be retrieved from that address. RAM is a term for all memory that can be read from or written to in a nonlinear fashion. The chip comes with no instructions in the chip.  When power is turned on the data can be moved in and out of the chip.  When power is turned off the chip loses all of its data.  The RAM chip is Volatile and that is the reason that we always have to save our data to an auxiliary storage device such as a floppy drive, hard drive, CD or EEROM.

RAM chips are used to temporally store data and  make up main memory. In human brains this is referred to as short term memory.  When some one says my computer has 512 Mega Bytes of RAM they are talking about main memory. All main memory is comprised of RAM chips.

Main Memory

Extended Memory 1 MByte up - 32 bit processor - 80386-1985,80486-1989,Petium I-1993, II-1997, III-1999, IV -2000.
High Memory - 640 KBytes  to 1 MByte - 20 bit processor - 80286 CPU 1983
Conventional Memory - 0 to 640 KBytes - 16 bit processor - 8088 CPU 1982

There are numerous types of RAM
    1) SIMM - single in line memory module
    2) DIMM - dual in line memory module
    3) DRAM - dynamic RAM
    4) FPM RAM - fast page mode RAM
    5) EDO RAM - extended - data out RAM
    6) BEDO RAM - burst extended data out RAM
    7) SDRAM - synchronous dynamic RAM
    8) SRAM - static random access memory
    9) Async SRAM - asynchronous SRAM
    10) PB SRAM - pipeline burst SRAM
    11) VRAM - video RAM
    12) WRAM - windows RAM
    13) SGRAM - synchronous graphics RAM

CMOS RAM Composite Metal Oxide Silicon Chip

Another type of specialized RAM chip is the Composite Metal Oxide Silicon chip.  This chip was first used with the 80286 CPU (IBM AT-1984) computer.  This chip has a battery attached so that when power is turned off the data on the chip will remain.  The cmos chip contains the set up data.  When you turn your computer on you will see instructions that say enter Alt-F10 or something similar to enter the set up program.

Input Unit: obtains information from input devices and places it at the disposal of the other units so that it can be processed.

Output Unit: takes information tht the computer has processed and places it on various output devices to make it available for use outside theomputer

Memory  Unit. rapid access, relatively low capacity wharehouse section retains information that has been entered through the input unit, making it immediately available for processing when needed.

Arithmetic and Logic unit(ALU) performs calculations, addition subtraction, multiplication and division. Decision mechanism that allow the computer to compare tow items from memory to determine whether they are equal.


Mathematical Operator Use
^ - exponential 3^3 = 27
* - multiply 3*3 = 9
/ - divide 5/2= 2.5
\ - integer division 5\2 = 2
mod - modular division 5 mod 2 = 1
+ - add 5 +2 = 7
- - subtract 5 - 2= 3
(  ) parentheses (  execute inside first )


Relational operators.

> greater than A > B
< less than A < B
>= greater than or equal to A >= B
<= less that or equal to A <= B
= equal to A = B
<> not <> A

Boolean Operators


A B C Result
True True True True
False True True False
False False True False
False False False False


A B C Result
True True True True
False True True True
False False True True
False False False False



B C Result
True True True False
False True True True
False False True True
False False False False


A Result
True False
False True

Operator Precedence used in evaluating expressions

High ^ Arithmetic
  Unary + or -  
  * / \ mod  
  +  -  
  <, >, <=, >=, =, <> Relational
  NOT Logical
Low OR and XOR  

CPU - Central Processing Unit  - coordinates and supervises the operation of the other units.

The CPU is the brains of the computer.  The CPU is responsible for all Input/Output I/O, Arithmetic, and Logic.

I/O - All input from devices such as keyboard, CD, HD, FD, touch screen, touch pad, writing pad, mouse, modem, network cable, video camera,  EEROM, tape drive, credit cards, etc. is controlled by the CPU. All output from the computer to printers, modems, monitor, disk drives, cd's, EEROM, tape drives, etc is controlled by the CPU.

Secondary storage unit.  program or data not actively being used by the other units are  placed on secondar storage devices - hard drive, etc.

Intel's web site http://www.intel.com/museum/index.htm?iid=about_intel+cr_museum
 will give you a history of the development of CPU's.