> On Feb 1, 2022, at 12:21 PM, Paul Koning via cctalk <[email protected]>
> wrote:
>
>> On Feb 1, 2022, at 12:16 PM, Mike Katz via cctalk <[email protected]>
>> wrote:
>>
>> 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.
I suspect CLV was invented for CDs, in fact. The reason is obvious: CDs
contain uncompressed digital audio, i.e., constant bit rate. If you want to
avoid big buffers -- an expensive thing to have in 1980s consumer electronics
-- the bits have to come off the media at essentially the desired payload data
rate. So you either use CAV with constant sector counts, which wastes a whole
lot of capacity given that the ratio of inner to outer radius is quite large on
a CD, or you go to CLV. The variable rotation rate is easy enough to handle
because CDs are accessed sequentially; the speed change on track switch is
small because track switches are only by +1 (during play).
You can often hear the RPM changes clearly, if you're asking the CD player to
do random access by skipping around the songs.
paul
