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Last month, we covered the basics of designing a custom PC system, and how to choose cases and power supplies. This time around, we'll go into how to choose motherboards and CPU chips.
The main circuit board of a personal computer is commonly known as the motherboard. All other "expansion cards" used in PC's plug directly into this board, both to draw power from the computer's power supply and to exchange information with the rest of the system. Because they plug into this main circuit board, in electronics lingo, expansion cards are also known as "daughterboards," while the main board is called the "motherboard."
To provide power to, and exchange information among, the various components, a special wiring system, or "bus," is used by the motherboard. The first such system to be standardized was called, "Industry Standard Architecture," or ISA for short. In 1992, a new wiring system, called "Local Bus," came onto the market. This system provides special, high-speed data circuits especially for the video graphics and hard disk subsystems. Because of the sheer quantity of information these two components handle, as PC's became faster and faster, more and more of the computer's time was being spent on transferring information between them. This caused the performance of the PC as a whole to suffer -- an effect similar to trying to drive on the freeway with the parking brake still on!
By setting up these high-speed data channels to handle only signals from the video graphics card and hard disk drive, the overall speed of the PC was dramatically increased. This arrangement was later codified by the Video Electronics Standards Association, or VESA, and is now commonly known as -- you guessed it -- "VESA Local Bus," or VLB. An even faster version of Local Bus, known as "Personal Computer Interface," or PCI, has come out with in the last year or so.
As important as the motherboard is, choosing the right Central Processing Unit, or CPU, is even more so. The CPU chip is the real "brain" of the computer, acting as a master control and coordinator for all of the PC's activities.
The first PC's had an 8088 CPU chip, made by Intel Microprocessors, Inc., or "Intel" for short. It had an internal clock that operated at a speed of 4.77 MegaHertz, or 4.77 million oscillations per second. As fast as that may seem, today's CPU chips operate at speeds of up to 100 MegaHertz -- nearly 25 times faster than the 8088.
You might think that the higher the clock speed of the CPU, the faster the computer as a whole will run. This is true, but only if the other components in the computer are designed to handle such speeds. Most of the PC components manufactured within the last year or two, thankfully, do have this capacity, especially if a VESA Local Bus or PCI Bus motherboard is used.
At the time I write this, the 486 and Pentium CPU's are the fastest and most popular, with the higher-speed 386 chips taking up the rear. (CPU chips are designated by a combination of the processor type and their clock speed rating. For example, the PC on which I'm writing this article has a 386 CPU, operating at 25 Megahertz, so it would be referred to as a 386-25. The additional term "DX-2" or "DX-3" between the chip type and clock speed indicates that special circuitry is being used to increase the CPU speed. Thus, the fastest 486 chips currently available are designated "486DX2/100," indicating an effective rate of 100 Megahertz.) For a multimedia system, such as we're putting together, at least a 486 CPU, operating at not less than 50 Megahertz, running on a VESA Local Bus motherboard, will be required. At this writing, prices for this combination range from about $200 to nearly $800, depending on the exact features you select. This is where your copies of "PC Catalog" and "Computer Shopper" will begin to earn their keep, as they will have information and advertising from a wide variety of suppliers. In this particular instance, one of the lower-priced VESA Local Bus motherboards, using a 486DX2/50 CPU, will be more than sufficient.
In our next installment, we'll cover the two subsystems that make the greatest use of VESA Local Bus architecture: hard drives and video graphics.
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