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SubjectRe: [OFFTOPIC] Re: disk head scheduling
On 22 Mar 1999, David Wragg wrote:

> "Richard B. Johnson" <> writes:
> > [snip]
> > Expensive disk drives now do full track buffering. This costs
> > money because RAM costs money. To buffer one full track on a
> > Disc drive requires CAPACITY / (HEADS * CYLINDERS) which can
> > be upwards of 100 megabytes of high-speed SRAM. Sector buffering
> > is always necessary. It is part of the de-serializer and is
> > required because the Disc internals are never synchronous with
> > the outside world.
> Why SRAM? The nice thing about SRAM is its low latencies. If you're
> slurping a whole track off a disk, latencies shouldn't be an issue;
> you might need lots of bandwidth, but you can get high bandwidth from

Because dynamic RAM needs refresh. Refresh takes power. You need
to keep the data without power, i.e., the bias from a small battery
that is essentially shelf-life.

> Static RAM? As in the stuff that L2 caches are made out of? As in the
> stuff that currently costs several times as DRAM for the same
> capacity?

That is very-high-speed, not needed here.

Dick Johnson
Penguin : Linux version 2.2.3 on an i686 machine (400.59 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.

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