On 24/10/2016 19:49, John Rumm wrote:
SNIP
Now in the case of a HDD there *may* be a relatively close mapping of
LBAs to physical sectors, such that as you step through sequential LBAs
it maps that to a physical address efficiently - addressing adjacent
sectors first, then heads, and finally cylinders. However even here
there is scope for redirection since the drives support bad sector
remapping etc. So two sequential LBAs may actually be stored in
completely different areas of the disk even with a HDD.
/SNIP
While logically adjacent sectors may be away off in the spares they're
not likely to be. I don't think I've ever seen as many as 1% faulty
disc. You can assume that most of the time they'll be next to each other.

Way back in the 1980s we had a report from QA that the new faster disc
drives were running slower than the old ones. On closer examination this
turned out to be one of the machines only. And it had a spare track in
the middle of the directory... which with CP/M is the _only_ directory...

Modern systems have lost the stuff we used to do, where we'd fiddle with
the interleave for performance, not have sector 1 in the same place on
each track, or skew the sectors across cylinders so a seek took you to
the new track just at the right place to sync up and read.

(not all at once!)

Andy