Although partially legacy-free designs have emerged at various times, no one has yet put all the pieces together and produced a PC that traces none of its hardware architecture to the original IBM designs.

But that's about to change. As the PC AT's 20th anniversary approaches, some vendors are already working on totally legacy-free designs that will finally do away with even such fundamentals as the BIOS--the basic input/output system that has booted every PC ever made since the original IBM PC design in 1981. (Yes, some legacy components go back even further than the AT. We'll come back to this point in a moment.)

Let's examine the major legacy components: we'll see where they came from, what they're evolving toward, and what it means for you. Strap yourself in--it's going to be quite a ride!

Bye-Bye, BIOS
The original IBM PC, introduced in 1981, contained the seeds of the design that would later (in the IBM AT of 1984) come to dominate PC architecture. This image (below), also scanned from an old Byte magazine, shows a photo of the actual hand-wired prototype motherboard for the original IBM PC--one of only two such prototypes built. That rough-looking circuit board is actually the forebear of all PCs ever made, an artifact as important as, say, Bell's first telephone or Edison's light bulb or the Wrights' Flyer.

The original PC's resemblance to today's PCs is less obvious than the AT's because some of the 1981 IBM PC's features--such as the port for connecting the PC to an audiocassette recorder for data storage--have fallen into obsolescence. But several other important components and features carried over to the 1984 AT design and have lingered ever since.

For example, even that first prototype PC had a BIOS that contained simple setup and diagnostic routines and controlled how the system booted and ran, exactly as it does in today's PCs.

To be sure, the BIOS has evolved over time. For example, unlike today's BIOSes, the original PC BIOS also contained a complete (albeit modest) software language, so users could do something with their PCs without having to load additional software from a slow cassette drive or from an expensive, optional floppy drive. This language was a version of Basic supplied to IBM by a then-little-known company called Microsoft.

Although the BIOS has evolved, it's still there at the heart of literally every PC ever made, an architectural component so deeply entrenched it may be the very last piece of the original IBM PC legacy to fade away.