From the early 1980s until about 1993 or so, many PCs supported only two hard disks.
For the first decade or so that hard disks were used in PCs, partitioning of a drive into multiple volumes was
not really done; as such, the two hard disks in a system were usually just "C:"
and "D:". BIOS code writers would often refer to these two drives as
"C" and "D". (Though in reality, drive
letters are dynamically assigned, and are not a matter of hardware at all.)
All modern BIOSes, since about 1994, have supported four IDE/ATA hard disks: two
channels (primary and secondary) and a master and slave device on each. Some actually
support more, and of course, additional IDE/ATA channels can be added to existing systems.
Any system that supports only two hard disks may theoretically be upgradable to allow
four-disk support. In practice, any system that old has at best a 486 processor and
probably very little system memory. Such a PC is so obsolete by today's standards that it
really isn't worth the effort. Find a low-demand use for the machine and get a more modern system; even a used machine a few
years old will be several notches above such an old machine.
Next: IDE/ATA Disk BIOS Settings
