Re: Disk geommetry, was Re: Kernel Upgrade: Why?
On Fri, Apr 23, 1999 at 08:50:40PM -0400, Dan Willard wrote:
>
> Think of it as a record (ya' know those old odd looking vinyl things).
> It spins at 33.3 rpm but the sound/music doesn't change from outer to inner.
> Same deal with hard drives although the outside is 'spinning' faster, it
> still picks up the same amount of data per rotation as it would near
> the center.
Actually, this is a good analogy, but the conclusion is wrong.
Hi-fi buffs (back when it was called hi-fi) knew that there was better
sound on the first tracks of LPs (near the outside). This was because
the vinyl was moving faster under the needle, which gave a better frequency
response at the high end i.e., more data about the music. In fact,
audio CDs slow their rotation on the outside tracks so they can play
back the data at a constant rate.
Hard drive manufacturers work in an incredibly competitive market. They
do their best to maximize the bits-per-square-centimeter density of the
platters in your drive. One great way they have found to do this is to
store more data on the outer tracks.
Older hard drives, MFM, RLL, early SCSIs and PC-format floppies don't
take advantage of this, however. My recollection is that the original
Mac 400K floppy was the first "personal" data recording device to use this
technique. I'm sure someone else can point out something the ancient
Egyptians did with it.
As a result, you get a much higher data rate on the outer tracks, with
the same angular latency as on the inner tracks.
- Marsh
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