(This document is part of the PC-Clone Unix Hardware Buyer's Guide. The Guide is maintained by Eric S. Raymond ; please email comments and corrections to him.)

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Motherboards

Provided you exercise a little prudence and stay out of the price basement, motherboards and BIOS chips don't vary much in quality. There are only six or so major brands of motherboard inside all those cases and they're pretty much interchangeable; brand premiums are low to nonexistent and cost is strictly tied to maximum speed and bus type. Unless you're buying from a "name" outfit like Compaq, Dell, or AST that rolls its own motherboards and BIOSes, there are only four major brands of BIOS chip (AMI, Phoenix, Mylex, Award) and not much to choose between 'em but the look of the self-test screens. One advantage Unix buyers have is that Unixes are built not to rely on the BIOS code (because it can't be used in protected mode without more pain than than it's worth). If your BIOS will boot properly, you're usually going to be OK.

The ``Baby AT'' motherboard form factor is obsolete. It's an ATX world now.

There are still a few potential gotchas to beware of, especially in the cheaper off-brand boards. One is ``shadow RAM'', a trick some boards use for speeding up DOS by copying the ROM contents into RAM at startup. It should be possible to disable this. Also, on a cacheing motherboard, you need to be able to disable cacheing in the memory areas used by expansion cards. Some cheap motherboards fail to pass bus-mastering tests and so are useless for use with a good SCSI interface; on others, the bus gets flaky when its turbo (high-speed) mode is on. Fortunately, these problems aren't common and are becoming less so.

You can avoid both dangerously fossilized hardware and these little gotchas by sticking with a system or motherboard design that's been tested with Unix.

Some other good features to look for in a motherboard include:

Gold-plated contacts in the expansion slots and RAM sockets. Base-metal contacts tend to grow an oxidation layer which can cause intermittent connection faults that look like bad RAM chips or boards. (This is why, if your hardware starts flaking out, one of the first things to do is jiggle or remove the boards and reseat them, and press down on the RAM chips to reseat them as well -- this may break up the oxidation layer. If this doesn't work, rubbing what contacts you can reach with a soft eraser is a good fast way to remove the oxidation film. Beware, some hard erasers, including many pencil erasers, can strip off the plating, too!)

The board should be speed-rated as high as your processor, of course. It's good if it's rated higher, so upgrade to a faster processor is just a matter of dropping in the chip and a new crystal.

If you're changing a motherboard, see the Installing a Motherboard page first. This one even has a Linux note.

Eric S. Raymond