Origin of "partition" in storage devices

[Paul Koning]

> On Feb 1, 2022, at 12:21 PM, Paul Koning via cctalk <cctalk at classiccmp.org> wrote:
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> 
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>> On Feb 1, 2022, at 12:16 PM, Mike Katz via cctalk <cctalk at classiccmp.org> wrote:
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>> In the rotating drive world there is constant linear velocity (CLV) and constant angular velocity (CAV) drives.
>> 
>> On CLV drives the speed of rotation would vary based on the track (slower in the inner tracks and faster on the outer tracks).  This meant that the data rate and number of bits/track remained constant.
> 
> Slower on the outer tracks, I believe.  CDs work this way.

More precisely:

CLV means slower rotation when positioned on the outer cylinders.  The outer cylinders have more sectors; the layout is such that the linear bit density is roughly constant, which in turn because of the constant linear velocity means constant data rate.

>> On CAV drives the rotational speed of the drive doesn't change, this means that the data rate and number of bits/track changes depending on the track.
> 
> It means that only if the sector count changes.  That's true for modern drives and for the CDC 6603; it wasn't true for quite a while.  A lot of "classic" disk drives have constant sector counts.  So, for example, an RP06 is a CAV drive and its transfer rate is independent of cylinder number since the sector count per track is constant.
> 
> I think hard drives are CAV as a rule because changing the spin rate as part of a seek takes too long.

Variable sector count is independent of CLV vs. CAV.  Modern drives have it, classic CAV drives mostly do not.  A CAV drive with fixed sector counts has fixed data rate; a CAV drive with more sectors on the outer tracks has higher transfer rate on those tracks.

	paul