Path: utzoo!utgpu!attcan!uunet!cbmvax!rutgers!mailrus!uflorida!gatech!linus!mbunix!eachus From: eachus@mitre-bedford.ARPA (Robert Eachus) Newsgroups: comp.sys.amiga Subject: Re: Request to Commodore (Bad Blocks) Summary: I think you have something here... Keywords: trackdisk.device Message-ID: <40244@linus.UUCP> Date: 23 Sep 88 16:05:01 GMT References: <8891@cup.portal.com> <5660018@hpcvca.HP.COM> Sender: news@linus.UUCP Reply-To: eachus@mitre-bedford.arpa (Robert I. Eachus) Followup-To: comp.sys.amiga.tech Organization: The MITRE Corporation, Bedford, Mass. Lines: 58 Suddenly a light bulb appears over my head, switched on and shining brightly. Charles has had a brilliant idea, and like most great ideas it only seems simple IF you understand it. > ------------------------------------------------------------------- > * DO NOT CHANGE THE WAY YOU READ. ONLY CHANGE THE WAY YOU WRITE. * > ------------------------------------------------------------------- >Therefore READS TAKE THE SAME AMOUNT OF TIME whether the writes are >decoupled from the index pulse or not. This is the key insight. Writes can be coupled to the index pulse, and disks written by a "smarter" trackdisk.device can be read (and written to) by an old trackdisk.device with NO compaibility problems. >We gave up track reliability for at best a 7% increase in overall >floppy speed. Not quite, Charles, adding track reliablity won't cost even that much. Right now, trackdisk.device must rewrite an entire track even if only one sector is changed, and more important must read a track completely to write one sector. If a "smart" trackdisk.device knows where sectors are located, it can do single sector writes in an average of 0.7 rotations, instead of 2.2. For compatibility reasons it should not do this on non-FFS floppies, but if a floppy is FFS then there is no reason to allow for the "old style" writes. This means that ALL accesses would be as fast or faster except formatting and full track writes. >It amazes me how easy it is to respond to a note without reading it. Most of us (including Ford) try hard to UNDERSTAND what the author had in mind before responding. In this case, I think that the net traffic should be taken as evidence that some ideas are very hard to explain. In fact, since many people probaably don't understand yet, let me take another try. The key insight from Charles is that the model of the medium need not be the same when reading as when writing. When reading it is sometimes useful to ignore some of the rules which must be obeyed when writing. In this case the hang-up that most of us have is that if tracks begin at the beginning they must be read from the beginning. Okay who is going to be the first on his block to hack up trackdisk.device and try this for real? And please, Commodore, require that FFS sectors be keyed off of the index so that the "incompatible" fast single sector writes can be supported, even if the implementation of such writes has to wait for 1.5. Note that this feature really will have a significant impact on performance, since it will often be used to update directory entries. Robert I. Eachus with STANDARD_DISCLAIMER; use STANDARD_DISCLAIMER; function MESSAGE (TEXT: in CLEVER_IDEAS) return BETTER_IDEAS is...