You can have N swap partitions on a drive -- it's just a matter of
configuration.  Changing from /dev/sd0a to /dev/dsk/c0t3d0s0 really
doesn't buy you anything, and it's a pain in the ass to type.
What's so "magic" about /dev/sd0a as opposed to /dev/dsk/c0t3d0s0?

You say that SVR4 let you have two swap partitions on one drive (never
mind why anyone would want to do that unless the partitions were
contiguous and one wanted to avoid redefining the partition table).
You can do that with BSD as well -- in fact, I have done such a thing
because I wanted my /tmp to be a swap-based fs.  At first, in preparation
for such a move, I had swap on sd0b and /tmp as a UFS on sd0d.
One day, I just decided to change sd0d to a swap partition and mount
/tmp on swap, and voila.  No problems.

I could have done this with any other partition, though I think
performance is significantly better if the two partitions are adjunct.

In short:  We have a partition table on the disk.  We don't swap to
slice 0 or 2 / partition a or c because, historically, that would erase
the label (does this still happen?).  So we put something meaningful
there and start swapping on slice 1/partition b.  It's just much easier
to type /dev/sd0b than it is to type /dev/dsk/c0t0d0s1.  I know what
"sd0b" means -- does anyone else have difficulty with this?

If anyone wants to jump in on this thread, let's take it to e-mail.
I'm not so sure it belongs here anymore.

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