Messages in this thread | | | Date | Mon, 22 Mar 1999 12:01:45 -0500 (EST) | From | "Richard B. Johnson" <> | Subject | Re: [OFFTOPIC] Re: disk head scheduling |
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On 22 Mar 1999, David Wragg wrote:
> "Richard B. Johnson" <root@chaos.analogic.com> 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.
Cheers, Dick Johnson ***** FILE SYSTEM WAS MODIFIED ***** 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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