The Babbler <bt...@babbleon.org> types:

BSD does it this way because the Unix it was based on did it. This dates back to at least v6, where I first met it. Root and swap used to be wired into the kernel at config time, and making the first two partitions the system had to find while booting the first two in the table does make sense. C was required and unusuable; it included the cylinders that were reserved for bad block handling, and the tools that did that assumed it was there. It was also used for disk-disk backups at times.

At the time, computers were typically used by more than one department at a time. This led to even more reasons to want to partition a disk. If memory serves, partition table information used to be in the kernel - wired into the driver for that disk - so all disks of the same type had to have the same partition table. So it was useful to stagger the partition sizes to provide more choices. A typical setup might have f, g and h about the same size and covering the entire disk. e was what was left in f after a & b were taken out. d was the usable disk beyond a & b (or something like that).

The only thing that's still hardwired is that root has to be on a. The boot sequence is fubar if you don't do that, though it's been claimed that that's not hard to fix. The rest you can do pretty much any way you please. I.e. - you don't need swap at all, and I've got one system that has swap on a different slice than it's root file system.

<mike