Cpu Bios Support

As a general rule, a BIOS does not need to include extensive support for specific models of CPU. Typically, if you use a CPU that's not supported by the BIOS, the worst that happens is that the CPU is misidentified when the system boots. There are exceptions to this rule, however, such as 2

• Some advanced 80486 CPUs support cache modes that can cause data corruption if ^ they're not supported by the BIOS. For this reason, you should only use CPUs such as T the AMD and Cyrix 5x86 on motherboards that are built for these CPUs. R

• The Cyrix 6x86, 6x86MX, and MII CPUs support a special linear burst mode that can A improve cache memory access times. This feature requires BIOS support. If this support SS is absent, the CPU still operates, albeit at a slightly slower speed than it would otherwise.

If your motherboard lacks support for a new CPU and you want to add that support, you should check with your motherboard manufacturer to see if an updated BIOS is available. Modern motherboards support a flash BIOS feature, in which you can update the BIOS by running a special DOS program. On older computers (mostly early 80486 systems and earlier), you may need to physically replace the BIOS chip, which is usually labeled with the distributor's name (see Figure 2.3).

BIOS flash utilities typically run under DOS. If you don't normally run DOS or Windows 9x on your computer, you can run the flash utility from a DOS boot floppy—in fact, this is the recommended procedure even if you have a DOS partition on your computer. If you don't have a DOS boot floppy, look into FreeDOS (http://www.freedos.org), an open source version of DOS. Do not attempt to flash your BIOS using DOSEMU under Linux!

BIOSes come from a variety of sources, but each BIOS is customized for a specific model of motherboard. You therefore should not attempt to use a BIOS for one brand or model motherboard in a different product, even if the BIOSes are from the same company. If you need help locating a BIOS for your motherboard, check with the motherboard manufacturer (the BIOS producer isn't likely to be able to help), or check Wim's BIOS Page (http://www.ping.be/ bios/), which includes information on BIOSes for a wide variety of motherboards.

Part i

Figure 2.3

BIOS chips come in a wide variety of shapes and sizes, but in most cases they're clearly labeled with the BIOS distributor's name—Award, in this case.

Figure 2.3

BIOS chips come in a wide variety of shapes and sizes, but in most cases they're clearly labeled with the BIOS distributor's name—Award, in this case.

Caution

Flashing a BIOS is a potentially dangerous undertaking. If there's a problem, such as a power failure during the operation or if you flashed the wrong BIOS, your computer may be rendered unbootable until you replace the BIOS chip with one that's been programmed by the motherboard manufacturer. I therefore recommend that you flash a BIOS only during normal business hours, and that you keep a backup of a working copy of your BIOS on a floppy. (Most BIOS flash utilities give you an option to create such a backup before flashing a new BIOS.) That way, you may be able to get help from a computer store if something goes wrong.

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