MAINBOARDS - Overview
Mainboards
The mainboard (also called the motherboard) is the single most important part of your computer. It determines what size and speed your CPU can be, how much RAM you may use, how many and what kinds of cards may be installed, what kind of mouse or keyboard you may use and the sex of your firstborn child. Well, it's only a computer part, so I guess it really doesn't have anything with sex or children or anything like that. I suppose. Not that I know of, anyway.
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Microprocessor
The term "CPU" (Central Processing Unit) is vague. It refers to the logical component of a computer system that interprets and executes program instructions. It is synonymous with "computer", or "processor" or "microprocessor". We use it here to refer to the microprocessor.
Each type of mainboard is designed around one type of CPU. A mainboard designed to use a Pentium Pro processor won't accept a 486, or a Pentium II/Celeron CPU, or even a Pentium CPU - it can ONLY use a Pentium Pro CPU. That's because each CPU is designed and built a little differently. They are each of different sizes, have more or fewer pins, and have far different electrical needs from each other. Even CPUs of the same type can have differing voltage and clock speed requirements, but those things can usually be adjusted on the mainboard by the use of jumper blocks, switches or internal electronic control.
To read more about CPU's, use the link at the bottom of this page
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RAM Modules
How much RAM (Random Access Memory) a particular mainboard can use is determined at the time the board is designed. There are sockets on the board that will accept RAM modules - 30 pin SIMM (Single In-line Memory Module) sockets on the older 386 & 486 boards, 72 pin SIMM sockets on some of the later 486 boards and most of the earlier Pentium boards and 168 pin DIMM (Dual In-line Memory Module) sockets on all the newest boards.
Many mainboards have more than one type of socket - for instance some of the latest Pentium class mainboards and most of the Pentium II/Celeron type mainboards have both the 72 pin SIMM sockets and the newer 168 pin DIMM sockets. The chipset (the other chips soldered onto the mainboard that work with the CPU) and the BIOS (Basic Input/Output System) of the mainboard determine how large (how much memory) each RAM module can be.
To read more about RAM, use the link(s) at the bottom of this page.
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EXPANSION SLOTS
There are a number of card sockets, called expansion slots, installed on the mainboard.
There are only 2 main types of slots: ISA and PCI, with ISA being phased out in the newest mainboards.
The ISA (Industry Standard Architecture) expansion slot was the first. It was the standard used by the first IBM-PCs and was used with the 8 bit bus used with the first CPUs. When the CPUs progressed to handling 16 bits at a time, the 16 bit ISA expansion slot came into use. (A bus is the pathway between microprocessor and expansion slots and memory.)
The next (and latest) standard is the PCI (Peripheral Component Interconnect) Expansion Slot which can use a 32 bit or a 64 bit bus. As home computers were growing from their 8 bit CPU origins to the 32bit/64bit CPU's of today, several options were offered for bus expansion (usually by IBM - it seems like they had a hard time accepting the fact that when they went in a certain direction, the rest of the world didn't necessarially have to follow). The best examples are IBM's MCA expansion slots and the VESA expansion slots. Both were superior to the 8 bit ISA bus and yet neither made it into the modern era. IBM's MCA (Micro Channel Architecture) offering was, in fact, an excellent idea and could easily have been what we would all be using today except IBM wanted everyone in the world to give them money every time it was used. We use PCI today and MCA is an IBM backwater that is being, or has been, phased out even by them. Another short lived 32/64 bit expansion slot was the EISA (Extended ISA), adapted by the industry but quickly replaced by the PCI slot.
There are at least 3 more slots that may be on a mainboard. One is another expansion slot that is designed strictly for video cards; it is called an AGP (Accelerated Graphics Port). Another would be a slot for modern microprocessors; a Slot 1 designed for Pentium II & III or the Slot 2 for the Xeon processors. The third slot that may be on your mainboard is a slot for an L2 Cache card - this will probably only appear on certain Pentium (socket 7) mainboards.
To read more about expansion slots, use the link at the bottom of this page.
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Built-ins vs Add-ons
Modern mainboards have a number of things built into them that early boards didn't - notably ports (serial and parallel) and disk controllers. Because more and more electronics is shrinking and more and more stuff is getting shoved into each chip, there are things being built into modern mainboards that have always been on expansion cards in the past. It's easy to find new mainboards with any or all of the sound card, video card, network interface card, SCSI card and modem built in. The advantage is in convenience and price. If it's built-in you don't have to install it and it's a whole lot cheaper to build it in at the factory than it is to add it on later. The disadvantage is flexibility. If your built-in whatever goes bad or becomes outdated, you can't replace it. All you can do is disable it in the setup and install a new one in an expansion slot - IF you have a free expansion slot! If not, you either get along without it or get a new mainboard.
My personal prejudices tend toward the less-built-in, more-expansion-slot side but it's easy to see why that's not going to be mainstream thinking in the future. Most consumers don't want to know what's inside the box - they want to plug it in, turn it on and do their thing. And modern electronics is extremely reliable. By the time something fails or becomes obsolete in a modern all-built-in (E-Box type) computer, the consumer will probably have already replaced it with a newer model.
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Ports
Ports are a method of getting information into or out of a computer. Serial ports have a single input or output line where information is fed in (or fed out) in a stream, one bit following the next. A mouse, an external modem and things like a digital camera or a PDA docking station are examples of devices that would use a serial port.
A parallel port, on the other hand, has 8 lines that information travel on at the same time. To transmit a byte (8 bits, remember?)out a serial port, it goes out 1 bit at a time - out the parallel port information is transmitted 8 bits (or 1 byte) at a time. A printer is the most common parallel port device, but you may also find scanners, tape back-up units, ZIP or SuperDisk Drives and a host of other things as well.
Other ports you might find on the mainboard are PS/2 type mouse or keyboard ports, IR (Infra-Red) ports or USB (Universal Serial Bus) ports.
To read more about Expansion Slots and Ports, use the link at the bottom of this page.
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Cards
Inside your computer, connected to the mainboard and to the outside, are various cards.....Sound Cards, NIC, Video Cards, etc. They each have a special purpose to make your computing experience possible. For example, without a Video card your monitor would not work, without a Sound card you couldn't listen to music on your CD-ROM.
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Conclusion
Mainboards are designed and built for a particular type of microprocessor but there can be a large variety within that type. An example would be the Pentium type micropressor. There are two main types of Pentiums designed and produced by Intel, several more from AMD and yet more from Cyrix. Each of these different types of Pentiums require different voltage settings and all were produced in a variety of speeds. So the designers of the mainboards had to be able to accomodate a basic Pentium micropressor with 5 or more basic voltage settings and more than 5 speed settings.
They accomplished this in several different ways. The first (and cheapest) way was to put pins on the main- board that would accept a jumper block - a series of pins either shorted together with jumper blocks or open (no jumper blocks) allowed choices to be made and implemented by the end user. The second way was to use small blocks of switches to accomplish the same thing. This was a little more expensive and switches go bad (which jumper blocks don't), so this was never a very popular choice except on the more expensive boards.
Today's boards use internal electronic controls with the settings stored on EEPROMs. Easy to set, easy to check and no moving parts.
All the above discussion has been about universal type mainboards - an average mainboard in an average, no-name type computer. The mainboards used by some companies are specially designed and built and will only fit in their especially designed cases. They won't look like an average mainboard and they can't be replaced with an average mainboard - they can only be replaced with an especially designed board from the same company. That's not necessarially all bad, but I'll take my chances in a free, open and competetive market rather than depend on a single source to treat me fairly.
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Additional Information may be found:
CPU's
Memory
Bits and Bytes
Expansion Slots and Ports
Other Expansion Cards
Sound Cards
Video Cards
Other Expansion CardsTo return to this screen, use the Back Button at the upper left hand side of your screen. It looks like this:
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