Origin of "partition" in storage devices

[Fred Cisin]

Many/most? early drives were CAV (Constant Angeular Velocity) with the 
same amount of data on each track.

Therefore, the data transfer rate, once on the right track, was the same.

BUT, the bits were physically closer to each other on the inner (higher 
numbered) tracks, and the error rate was sometimes noticeably higher on 
the inner tracks.  (and hence TG43 on 8"drives)  That was why most OS's 
would allocate space starting at the outside (lower numbered) tracks, and 
only use the innermost tracks when necessary.  With no errors, inner and 
outer tracks were the same speed. BUT, if you count RETRY's on a less than 
a perfect disk, then outer tracks had faster access than inner tracks.


In addition, track to track step times were conservative, often without 
knowing what step rate the drive could do, to allow plenty of time for 
completion and settling. In fact, one of the changes from PC-DOS 2.00 to 
PC-DOS 2.10 was to slow the step rate, because the Qumetrak 142 drives in 
the Convertible and PCJr were much slower.

Some floppy drives could do a "Recalibrate" (seek to track 0) much faster, 
and use a track 0 sensor to know when it had arrived.  Many OS's, when 
they encountered a "SEEK ERROR" (reading the track shows a different track 
number than desired), would RECALIBRATE and then step by step seek back to 
the desired track, rather than calculating how many tracks they were off. 
Because of that, access time to get to the desired track was sometimes 
faster for the outer (lower numbered) tracks, due to detours to track 0.

Since the DIRectory gets accessed more than any other location, access 
time to the DIRectory track is especially important.
Some OS's, including Microsoft Stand-Alone BASIC, COCO, etc. put the 
DIRectory at the seek center. So long as there were no "SEEK ERROR"s, that 
was faster, but when there WERE "SEEK ERROR"s, putting the DIRectory on 
track 0 (such as MS-DOS and Mac) was faster.