Path: utzoo!utgpu!attcan!uunet!ncrlnk!ncr-sd!hp-sdd!hplabs!nsc!voder!apple!keith
From: keith@Apple.COM (Keith Rollin)
Newsgroups: comp.sys.apple
Subject: Re: GS/OS
Message-ID: <18524@apple.Apple.COM>
Date: 10 Oct 88 16:44:59 GMT
References: <8809302002.aa26185@SMOKE.BRL.MIL> <3678@dad.UUCP> <9773@srcsip.UUCP> <18409@apple.Apple.COM> <15161@agate.BERKELEY.EDU>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 37

In article <15161@agate.BERKELEY.EDU> c60c-3aw@web-3d.berkeley.edu (Andy McFadden) writes:
>In article <18409@apple.Apple.COM> keith@Apple.COM (Keith Rollin) writes:
>>In article <9773@srcsip.UUCP> shankar@ely.UUCP (Subash Shankar) writes:
>>>Does anybody know what the benefits of the disk caching NDA under GS/OS?
>[stuff removed]
>
>>The GS/OS RAM cache is for the most recently and most frequently used blocks
>>read from disk. Since you are reading each block only once, the benefits of
>>a cache are not achieved; this is NOT a READ AHEAD cache.
>
>I get the impression it doesn't do the "read entire track" trick that
>Diversi-Cache uses... if not, why not?
>

It may be an indication of things to come. As you may have heard, GS/OS
supports files that have "data" and "resource" forks. A data fork is just like
the data in files that we all know and love, and resource forks are like a
database of small bits of information associated with every file.

On the Macintosh, we found that the best type of cache to implement was the
kind described above. This was becuse most access to the disk were for these
small resources. Each resource is typically less than a block long. Therefore,
the assumption that Diversi-Cache makes that all of the information on the
track is going to be needed is incorrect. By caching just the blocks needed, we
get better performance.

Now, this certainly isn't currently true for GS/OS, but it might be in the
future. I think that the GS/OS engineers were just thinking ahead.



Keith Rollin                               UUCP:      amdahl\
Developer Technical Support                      pyramid!sun !apple!keith
Apple Computer                                        decwrl/
                                         BITNET: keith%apple.com@relay.cs.net
"You can do what you want to me, but leave my computer alone!"