Xref: utzoo comp.sys.apple2:412 comp.sys.apple:23818 Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!tut.cis.ohio-state.edu!pt.cs.cmu.edu!andrew.cmu.edu!cs4w+ From: cs4w+@andrew.cmu.edu (Charles William Swiger) Newsgroups: comp.sys.apple2,comp.sys.apple Subject: Re: Interleaves, was: Fast reading of floppies... Message-ID: Date: 24 Mar 90 15:36:29 GMT References: <1990Mar15.142012.15985@spectre.ccsf.caltech.edu> <13979@nigel.udel.EDU> , <9891@wpi.wpi.edu> Organization: Carnegie Mellon, Pittsburgh, PA Lines: 48 In-Reply-To: <9891@wpi.wpi.edu> Quotes are from Dave Seah: "There used to be a disk copier called Disk Muncher that just read in the raw data without decoding it, then writing the stuff back out directly. It was real fast, but somewhat unreliable." Disk Muncher is still useful. It copies Infocom games flawlessly, without any parameter changes, and without using the one-track-at-a-time bit copier of Copy //+ (major time-saving tip here). As for it being unreliable, I don't remember it producing many bad copies. "I've always wondered if the 3.5" is really continuously variable. When you listen to the mechanism format a disk, it seems like the drive produces 5 or 6 different motor hums...is the drive capable of only 5 or 6 different discrete speeds? Continuously variable seems to be like overkill." The drive motor wouldn't have to be continuously variable, it would just have to be able to rotate at 80 different speeds. And yes, that definitely would be overkill (explanation below). However, my article was intended to be a non-technical introduction to interleaves, so I generalized a bit, and ignored the specific details (and I said I was doing so!! ;-). The general idea was that the drive changed speeds on the outer tracks in order to take advantage of the greater length available, thus being able to store more information of the disk then if the drive rotated at a constant speed. There's a reason why the drive only changes speed a couple of times. It would be pointless to change the drive speed if you can't fit another block onto the track (that's the reason for changing the speed, remember?) You'd only make the sync fields a little larger. So it's no surprise that the drive speed only changes when you actually can fit another block on the track (which means you only change speed a couple of times, as you say). Actually, it's easier to make a motor continuously variable then to make one that steps from one speed to another. The speed of a DC motor depends on power (volts times amps), so all you would do to make one continuously variable is to drive the motor off an amp (or just a transistor, same difference) whose input simply varies with the drive speed you want. To make one step from one speed to another would require some digital counting circuitry and a D/A converter, as well as the amp to drive the motor. -- Charles William Swiger