"Jay Levitt" wrote in message
...

I'm Pretty Sure I Read Somewhere(TM) that they still do that...

There seems no reason for it any more.

In the old days, data transfers were small, typically one tenth of a track.
Usually, the CPU was not fast enought to issue a read request in the time
between one read finishing and the start of the next block coming under the
read head. So it would take ten disk revolutions to read a track if the
blocks wereread one at a time in sequential order. By interleaving to match
the CPU speed, the CPU could read two or three or maybe more locks per
revolution, so disk transfers speeds for larg files improved.

But sometime in the 1990s, disks started to include buffers. When the CPU
reads a block, the disk itself stores the following blocks to the buffer; so
there's no rotational delay for subsequent block reads anyway, hence no
point in inteleaving. And of course computers have much more RAM thesedays,
and can easily allocate enough to read entire large amounts of data at a
time.

Tim