💾 Archived View for mirrors.apple2.org.za › archive › apple.cabi.net › FAQs.and.INFO › GSOS › gsos.c… captured on 2023-03-20 at 22:50:15.
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Newsgroups: comp.sys.apple2 Path: news.weeg.uiowa.edu!news.uiowa.edu!hobbes.physics.uiowa.edu!zaphod.mps.ohio-state.edu!wupost!cs.utexas.edu!uunet!decwrl!apple!mumbo.apple.com!gallant.apple.com!kip2-58.apple.com!user From: mattd@apple.com (Matt Deatherage) Subject: Re: RamFAST & GS/OS cache Sender: news@gallant.apple.com Message-ID: <mattd-251192182232@kip2-58.apple.com> Date: Thu, 26 Nov 1992 02:30:20 GMT References: <fmlin.2bnm@terapin.com> <1992Nov24.071645.9523@actrix.gen.nz> <1et4i7INNht6@gap.caltech.edu> <74677@apple.apple.COM> Organization: Developer Technical Support, Apple Computer, Inc. Followup-To: comp.sys.apple2 Lines: 47 Dave's already come and corrected a lot of the garbage in this thread, but it _never_ ceases to amaze me how people I usually respect and admire can throw garbage around like it was fact -- when it comes to the GS/OS cache. More intelligent people have more stupid ideas about this one piece of software than anything else I've ever seen. There have been some good facts in here, but it's hard to pick them out from the rest of it. I wrote an article nearly three years ago for _develop_ explaining how the cache works; it was published in _develop_ #2. It's been on every Developer CD since April 1990. If you want to know how things work, go read the article. Drew's current driver is 100% correct to not use the cache at all. If it's faster to return information from the media than to search the cache and copy it, there's no reason to use caching. The RamFAST driver doesn't use caching for this very reason. To suggest that it should be changed due to some mystical belief that GS/OS's cache knows better than an individual device driver is misinformed at best. Someone said the Apple SCSI card doesn't cache at all. Rubbish. It uses the GS/OS cache like other drivers. Not having an onboard cache, this makes the most sense for the driver. Todd suggested that FSTs should read cache memory directly; this is a bad idea. Dave is right on target -- if that happened, devices wouldn't have a way to detect media swaps and flush the cache, and you could get blocks belonging to a disk you ejected a while back. Drivers can't notice disks are ejected until someone calls the driver and gives it code time -- right now, they get that on every read call and the driver manages the cache. That's why it works. Similarly, the comment that GS/OS caches "everything" or "directories" is also rubbish. An FST asks a driver to cache things it thinks it might want again but doesn't want to keep around -- or things that an application requests are cached. The driver can then decide whether it's smart to cache those things or not. There's good background in the article "Demystifying the GS/OS Cache" in _develop_ #2. If you have questions, please dig it out and read it. ============================================================================ Matt Deatherage, Developer Support Center, Apple Computer, Inc. Personal mail only -- please POST technical questions, questions about Apple and its policies, where to find documents and related inquiries. The opinions I express don't represent Apple, which makes us both happy. ============================================================================