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Posted by Bill Vermillion on 01/02/06 17:45
In article <9irdr1h544obpnavenftu89u82ob7dhd7l@4ax.com>,
Roy L. Fuchs <roylfuchs@urfargingicehole.org> wrote:
>On Sat, 31 Dec 2005 18:55:01 GMT, bv@wjv.com (Bill Vermillion) Gave
>us:
>
>>In article <h8o9r199qbn2m24llsdm71fpeikiite3fv@4ax.com>,
>>Roy L. Fuchs <roylfuchs@urfargingicehole.org> wrote:
>>>On Fri, 30 Dec 2005 06:15:01 GMT, bv@wjv.com (Bill Vermillion) Gave
>>>us:
>>>
>>>> That was nice for the CLV movies that were only
>>>>1/2 hour per side.
>>
>>> CAV movies were the 0.5 hr per side individual frame versions, not
>>>CLV.
>>
>>Sorry - my brain mis-fired.
>>
>>I do know better than that.
>>
>
>
> I figured you did.
>
> CAV is the visibly sectored, single frame per revolution Constant
>Angular Velocity disc. CLV is the WORM type session that gets slower
>and slower as the laser progresses to the outer edge of the disc in
>order to keep the bit rate the same, hence the name Constant Linear
>Velocity. Since the pits are all the same length.
Actually the pits won't be the same length as they are just
representations of a clipped FM signal. So the pit length will
vary directly with the frequency at that instant. But the tracks
will be the same length.
> The older hard drives (different subject)actually had a poorer
>lineal density at the outer cylinders. CAV LDs do as well. They got
>rid of that with the advent of RLL platter formatting in the hard
>drives. LDs that are CAV still must have only one frame per
>revolution. Two fields.
Don't confuse HDs and their RLL [ actually MFM on floppies is
a from of RLL in a 1:3 mode while the first HD RLLs that were
adverstised as RLL were 3:7 as I recall ] as that has to do with
bit representation - while LDs, as I said above, are the FM signal
that is clipped. Then when read back the original FM signal is
regenerated. LDs are an analog medium.
And virtually all digital media use forms of RLL to increase the
data as the 0's are computed from the length of time it takes from
the last change - either from pit to land - as the change is
taken as a '1'. It's amazing how many changes have come from the
days when each bit on a disk had an intervening clock bit to keep
things synchronized.
And actually if I'm not mis-remembering too badly, the CLV was
_technically_ replaced by CAA - Constant Angular Acceleartion -
which was done to elminate herring-bone interference that was
happenind with CLV when they tried to get more info on the disk.
They still call the disks CLV because that was known, but CAA is
actually a series of CAV that change every few revolutions.
For some reason my memory says this was first done about the time
that Blazing Saddles was released.
I think I've been around this stuff too long. Last week marked
the 27th anniversary of my first home computer - which was about 9
months after my first VCR.
Bill
--
Bill Vermillion - bv @ wjv . com
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