From: stuarta@syd.dms.CSIRO.AU (Stuart Andrews)
Subject: IBM-PC Tute
Keywords: Lesson 1
Organization: CSIRO Div. Maths & Stats, CSIRO Div. Applied Physics
Distribution: aus
Date: Tue, 17 Nov 1992 07:31:18 GMT

How to make your own IBM Compatible Personal Computer. 
------------------------------------------------------ 
Lesson 1. The computer Motherboard. 
 
 
 |Connector for 
 |power supply 
 v 
 ------------------------------------  
| ooooo                              | 
|                                    | 
|                                    | 
|] <-Keyboard connector              | 
|                                    | 
|                   === <- co-processor 
| =========         ===              | 
|                   ---<-processor   | 
| =========         | |              | 
|                   ---              | 
| ========= ====                     | 
|                                    | 
| =========                          | 
|                                    | 
| ========= ====                     | 
|                                    | 
| ========= ====       []   = = = =  | 
|                      []   = = = =  | 
| ========= ====       []   = = = =  | 
|                      []   = = = =  | <- Memory (RAM) 
| ========= ====       []   = = = =  |    Usually a couple 
|                      []   = = = =  |    of dozen. 
| ========= ====       []   = = = =  | 
|                      []   = = = =  | 
|                                    | 
 ------------------------------------  
 
   ^                    ^
   |                    Memory (ROM) 
   Expansion bus        May be from 1 to eight 
   slots 
---------------------------------------------------                             
 
MEMORY (RAM) Rows of small chips. Usually 4,6,or 8 rows of 8 or 9 
chips. Markings usually include something like 41256 or 41128 or 
41512 (a number that is a multiple of 2 (2,4,8,16,32,64,128 etc) 
They hold the computers working memory while it is switched ON 
but lose everything when off. Sometimes there is space to 
add more chips. In more modern motherboards, RAM will be fitted in
the form of several plug-in modules (SIMMs or SIPs) which are
small printed circuit board which stand up on the motherboard.
 
MEMORY (ROM) One or more chips (maybe with a glass window) maybe 
marked 27128, 27256, 27512 etc or if it has a sticker, the 
word "BIOS" or something like. A big chip (about 2 x 5 cm), 
this/they hold the computer's basic startup program. ROMs 
do not lose their memory when turned off so this is the first 
place the computer looks for what to do when turned on. 
 
POWER SUPPLY CONNECTOR. A row of about 8 or 10 pins to connect 
by a cable to the power supply. The p.s. is a big silver box 
with a fan in it, a switch and connects to the power point. 
 
PROCESSOR: Usually a square black chip. Marked 
"i80286-16" the 80286 is the type of processor, 
the -16 is the speed limit for the chip in megahertz (MHz) Also 
available, i8086 and i8088 (old types), i80386 (pretty good), 
i80486 (the best). Usually referred to by the last three numbers, 
ie; 286, 386, 486. 
 
CO-PROCESSOR: In the case of '286, the co-processor is a 40 pin DIP 
(long, thin). For 386 and 486, it is a square chip. Part numbers are 
i80287, i80387 and i80487. What do they do? They add the capability of 
doing floating point calculations to the computer. Usually, they can be 
done in s/w without the chip, but this way is much faster. Some 
programs *require* the chip, others will work around it, some s/w 
doesn't need it at all - check the individual s/w. Also called 
Math-co-processor, a more correct name. 
 
EXPANSION BUS: Used to plug in all new stuff like disk drive 
controllers, video (monitor) cards, mouse cards, joystick cards 
All jobs except for the basic computer are done by add on cards 
which all look quite similar, are the same shape, but have different 
electronics depending on what they do. More on these in Lesson 2. 
 
KEYBOARD CONNECTOR: Where you plug the cigarette lighter. What do
you reckon it does?
 
All of the above bits usually com already attached to the computer 
motherboard. (Although you often have to buy RAM and plug it in 
yourself (if making your own)) and none of these bits are left out. 
They may be re-arranged in different places. (except the Expansion 
bus and the Keyboard connector and the power supply connector) 
 
 
End of lesson 1. Next Lesson. Expansion cards. How to make the computer 
talk to the outside world. 
 



-- 
  "Two to the power of one hundred thousand to one against.
    That's pretty improbable you know" (Ford Prefect)

"I do not agree with what you say, but I will fight to the death
 for your right to say it" (Voltaire)
################################################################################
Stuart Andrews (stuarta@syd.dms.csiro.au)
Opinions posted here are mine and do not necessarily comply with those of CSIRO
Newsgroups: aus.computers.ibm-pc