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Date:	Mon, 2 Jun 2003 14:49:17 PDT7
From:	waynec@linkline.com
Reply-To:	scoug-help@scoug.com
To:	scoug-help@scoug.com
Subject:	SCOUG-Help: HDD cache size choice with OS/2

Content Type: text/plain

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Info 4 SYNass writes:

>
> If 8MB cache works with OS/2 then I do not hesitate to choose but
> I would choose 2MB cache if I know 8MB cache works with M$ only !!
>

Svobi, I would be very surprised if the operating system ever sees the 8mb
cache. My guess (and I have to admit it IS a guess, based on my mainframe
experience) is that the drive uses that cache internally to save data it's
recently read, and to read ahead one block further than the last record the
computer requested.

It likely transacts business with the computer the same way it would without
cache (ie, the cache is transparent to the computer). When it gets a read
request, it first checks the cache to see if the record is already there,
and if so, it doesn't need to move the heads to read the data... it just
transfers the data record from cache to the computer and then initiates a
read of the next sequential record in anticipation of the computer asking
for that record next. The larger the cache, the greater the chance that the
record the computer wants is in the cache.

In doing things like loading programs, or reading sequentially through data
in a recently-defragged partition, cache will speed up disk reads without
having to increase the mechanical speeds (seek, search, rotational delay) of
the drive.

I don't know if it does the same thing on writes, ie, accept the data, put
it in the cache, and tell the computer the record has been written, then
asynchronously write records as the cache fills up. If it does use cache on
writes, then there is a possibility of lost records if the drive were to
fail or your electricity goes out (but at that point you'd have bigger
problems to worry about).

Wayne

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