Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site peora.UUCP Path: utzoo!watmath!clyde!cbosgd!ihnp4!pesnta!peora!jer From: jer@peora.UUCP (J. Eric Roskos) Newsgroups: net.micro,net.arch Subject: Re: Apple's IWM; Floppy Disk Controllers Message-ID: <1894@peora.UUCP> Date: Mon, 6-Jan-86 08:56:15 EST Article-I.D.: peora.1894 Posted: Mon Jan 6 08:56:15 1986 Date-Received: Tue, 7-Jan-86 04:25:51 EST References: <382@ncr-sd.UUCP> Organization: CONCURRENT Computer SDC, Orlando, Fl. Lines: 48 Xref: watmath net.micro:13390 net.arch:2377 In response to my comments on Apple's "Integrated Woz Machine" (IWM), stubbs@ncr-sd.UUCP writes: > According to several articles I read on the Mac, Steve Wozniak takes > credit for this, it saved the price of a disk controller, and allowed > different rotation speeds controlled by software depending on whether the > track being accessed was inside or outside. This was to equalize the > density of information.They called this technique the "Wos Machine". Well, I'd like to expand on my puzzlement about this a little. A lot of publicity and user-enthusiasm has been generated over the years as a result of the "simplicity" of Apple's floppy disk controllers. "Look at this Apple II disk card," people say, "it just has a couple of gates and a ROM on it! Why are the cards in machines like the IBM PC so complicated?" But this doesn't make that much sense to me. It has been my impression (though I have never seen any concrete evidence of it) that most of the VLSI floppy disk controllers you buy from people like Intel are really just these 1-chip microcomputers that have been programmed to work a floppy disk drive. In any case, they are dedicated processors that spend all their time generating the control signals for the floppy disk, so the CPU can work on other things. Now, it is fairly obvious that you can also do all that with timing loops on the CPU; you can even go so far as Sinclair did with their ZX-81, and even generate the video signals in the CPU, for example. But it's not a matter of "here this engineer has designed this new floppy disk controller, see, it only has 3 chips!" It's a matter of eliminating some of the parallelism in the machine. Thus you get the reduction in chip count at a (sometimes considerable) cost in terms of performance of the machine, because now your CPU has to sit spinning around in timing loops whenever you do disk I/O, whereas before you had a dedicated processor to do that. Furthermore, it may be that a fully general CPU can't execute as fast as the one in the disk controller, so you lose even more performance that way. That seems to be a large part of the speed problem with the Macintosh; when you use more intelligent disk drives with it, or use a RAM disk, you get a considerable performance improvement, which *seems* to be due to the elimination of the overhead of the CPU doing all the low-level I/O. The improvement seems disproportionate to a similar improvement made by changing from floppy disk to RAM disk on an IBM PC, for example. -- UUCP: Ofc: jer@peora.UUCP Home: jer@jerpc.CCC.UUCP CCC DNS: peora, pesnta US Mail: MS 795; CONCURRENT Computer Corp. SDC; (A Perkin-Elmer Company) 2486 Sand Lake Road, Orlando, FL 32809-7642 "Oh, is he your friend? Ask him his name!"