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Motherboard Page

The motherboard sits in the computer case. It gets power from the power supply and provides power to the expansion cards and keyboard. The processor, memory and expansion cards are mounted directly to the motherboard. Some motherboards have a slot for a math co-processor, an add-on chip that handles mathematic operations to free up processing power.

There are two and two major divisions of motherboards. One of the major divisions is between XT, that is, 8088 or 8086 processor motherboards and AT and or 80x86 processor motherboards (where the x is 2,3,4,5 or 6;possibly 7+ soon). An XT motherboard does not support the AT bus and cannot take AT expansion cards. The second division is between standard and non-standard motherboards. IBM set the standards with their XT and AT PC's (Personal Computers). So, if your power connector or expansion board arrangement do not match the accepted norm, you have a non-standard computer. I will deal with standard configurations.

But wait. Now I have to add that there is another major advance in Intel processors. These newer, faster dual processors, the Pentium Pro and Pentium II. What's different, you ask. Well, the two are fairly similar in that they split the duties of reading information and writing it out. Internal processing is split between the two with the input handled by the first and output by the second. Another difference is that there are two processors instead of one. In one of the cases, I misrecall which, the processors reside on a circuit board that attaches to the computer in a way similar to a SIMM or an expansion card. All of the other stuff about processors still applies (except I haven't OWNED one yet so I have no picture to show you). Processors

The processor is the integrated circuit chip on the motherboard that processes data. Instructions, a computer program, sent to the computer tell the processor how to interpret the rest of the program and what to do with data. The processor may be soldered directly to the motherboard or may be mechanically inserted inside what is called a chip socket. It can usually be found by looking for one of the biggest chips on the motherboard, then reading the numbers and name on the chip. But, how does the processor know to begin processing and what to do when it begins?


The BIOS or Basic Input/Output System contains information that the processor needs to "see" the other parts of the computer. Before it loads Bubaloo's Bluegill Bowl Fishing in the Louisiana Outback, before you can load Windows, before DOS boots up the BIOS must boot up and let the processor know what is out there! An American Megatrends (AMIBIOS), Award, Phoenix BIOS or some other boots the processor before DOS boots the computer. The BIOS chip is hard-wired with certain default information. In an AT style computer, there is the addition of a CMOS (Complimentary Metal Oxide Semiconductor) memory that holds information about the particulars of its machine. A battery keeps the CMOS chip active when you shut down. CMOS chips, while too expensive to use for RAM (Random Access Memory), are ideal for this function because they require excruciatingly little power to hold information.


Random Access Memory (RAM) is where the computer holds information it needs immediately. Like programs. The computer loads the program into memory and runs the commands contained in the program. To run bigger programs, you need more memory. The new computers, and newer computer programs, pull a trick. They can store "pages" of information to disk instead of in memory. This is a neat trick, since we can't all afford to put 128 Megabytes of main memory in our computers. However, it can get BORING, waiting for the slow transfer of information to and from disk. This is why more memory can mean faster processing speed!

RAM is loaded differently on different motherboards. XT computers use DIP (dual inline pack) RAM chips. These look like any standard integrated circuit chip with leads on both sides. AT's started using SIP (single inline pack) memory and SIMMS (single inline memory module). Each of these has chips mounted on a wafer of printed circuit board with an edge-connector. The edge connector fits into a socket made for the purpose, with

Simm converter
metal contacts for power and data. Memory on an XT could usually be upgraded to 640 Kilobytes or 1 Megabyte. Modern computers can go upwards of 128 Megabytes.

SIMM's have grown in capacity and speed, thus the number of contacts. More data at a time can pass through the greater number of pins. 30 pin SIMMS have been replaced by SIMMS with 72 pins. To convert 30 pin SIMMS to 72 pin SIMMS a sim converter is used. It loads up with four or more SIMMS and slips into a 72 pin SIMM slot.

Some information is needed almost constantly. If a program is written correctly, Cache memory can be a great help. You see, cache memory is much faster than standard main memory. Using cache for the stuff that is needed again and again lets the processor access main memory only occasionally, when the need arises. This makes some programs faster. The more cache you have, the more effectively caching can work and the faster these programs will run. Cache memory looks much like DIP chips from the XT computers.

Eight bit XT Slot Sixteen bit AT bus

Expansion slots provide power and data connections to expansion cards. Expansion cards give a computer variety. A bare computer can be enhanced with a VGA video card, disk drive controller, sound card, modem and a variety of esoteric cards. Mostly, these communicate with peripheral devices like monitors, scanners or telephone lines. The expansion slots may be XT (8-bit), AT (16-bit), Vesa Local (32-bit) or PCI (64-bit) bus cards. The "wider" the bus (imagine lanes on a freeway) the greater amount of data transferred per processor cycle (also called a clock tick). An expansion card connected to the motherboard is also screwed down on the case to prevent it coming out of its slot. The metal contacts on an expansion card's edge connector are called "fingers". If the fingers are mis-aligned or not touching the corresponding contacts on the card's slot, the expansion card will not work properly. Always make sure expansion cards are correctly inserted in the socket.

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Updated January 24, 1998, 10:52pm.