While the 1-missippi, 2-miss... 3... idea of the sync's
sounds OK to me, I always thought it was due to the
possibility of a 3-level cache and a 1 level sync, that is,
that there could be multiple memory buffers in the
kernal, O/S and (any) applications that would each
make it "up" one level with each sync, So you had to do
it that many times to get all the way out to the disk.
Strictly a gut feel thing based on having to write my own
(app level) memory managers a couple of times.
John A.