The life and times of the modern motherboard

Posted at: Tuesday 27th November 2007 by Alex Watson

Ever wondered how a motherboard and its BIOS are designed and made? What makes one a brilliant overclocker and another as stable as a plate of jelly on a bouncy castle? Alex Watson investigates.

When it was released in 1981, the IBM PC was extremely popular, but the fact that IBM had used a lot of retail parts to create the machine meant that it was fairly easy to build a similar system. However, in order for these clone machines to be 100 per cent compatible with the IBM model, IBM's rivals needed to copy the BIOS of Big Blue's original.

Unfortunately, a court decision that was imposed when Apple sued a manufacturer of Apple II clones meant that you couldn't copy out portions of the BIOS code for your own use. You could however, reverse-engineer it. Compaq spent $1 million doing just that, so it could make its own 100 per cent IBM PC-compatible machines.

Other firms, including Phoenix, did the same and started licensing their IBM-compatible BIOS code to anyone who could pay (they still do - we'll come back to that later). Intel and Microsoft were happy to widen their market by selling their products to other outlets as well as IBM, thereby creating the modern situation in which people can buy compatible PC hardware from a variety of vendors.

With the market thriving, it wasn't long before open, compatible hardware standards were set, beginning with the original 8-bit ISA, through to PCI, AGP and now PCI-E.

The BIOS

Coding a BIOS that functioned identically to IBM's - and all its customers' - was crucial to ensuring total compatibility with IBM's machine. This is because a PC is more than its set of assembled hardware, and it's also more than its operating software. Something has to kick the hardware into life and bring it up to a functional level so that the OS can order it around. The job of the BIOS is to link the PC's two worlds: the hardware you run, and the software you see. 'A BIOS engineer must understand both hardware and software, as he controls every hardware function,' as Chen George puts it.

Alex Perng, who leads one of Asus' BIOS teams, explains, 'The BIOS commands the CPU, chipsets and other devices to work together, and makes the system bootable.' Stressing how essential this is to the PC, he says the BIOS is 'like the spirit of a human being'.

Taiwanese motherboard companies don't start from square one when a new board needs a new BIOS. The BIOS is a modular program, and the core modules are licensed from a BIOS house, usually AMI or Phoenix. Perng estimates these licensed parts comprise around 70 per cent of the BIOS, with the remaining 30 per cent being coded from scratch.

'The fixed BIOS source codes deal with legacy devices such as COM ports, and also include specification-related codes for IRQs, BBS and so forth. The 30 per cent new code we write is used to support new chipsets and add new features,' he explains.

BIOS teams aren't large; according to the Taiwanese firms with which we spoke, teamwork is essential for solving problems, but usually one or two engineers write a BIOS, and work on it for several motherboards at once.