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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
    > DRAM.

    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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