lkml.org 
[lkml]   [1999]   [Mar]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [OFFTOPIC] Re: disk head scheduling
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.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:50    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site