Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!cmcl2!rna!cubsvax!peters From: peters@cubsvax.UUCP (Peter S. Shenkin) Newsgroups: net.arch,net.periphs Subject: Re: Why optical disks are slow to seek; an idea for higher capacity disks Message-ID: <573@cubsvax.UUCP> Date: Wed, 5-Nov-86 15:36:03 EST Article-I.D.: cubsvax.573 Posted: Wed Nov 5 15:36:03 1986 Date-Received: Wed, 5-Nov-86 22:47:18 EST References: <1128@tekig5.UUCP> <5100141@ccvaxa> <553@cubsvax.UUCP> <2474@peora.UUCP> <1256@hoptoad.uucp> Reply-To: peters@cubsvax.UUCP (Peter S. Shenkin) Organization: Columbia Univ. Bio. CG Fac., NY Lines: 31 Xref: mnetor net.arch:3342 net.periphs:598 In article ccplumb@watnot.UUCP (Colin Plumb) writes: >They didn't carry it as far as possible, but Commodore varied the clock rates >on their 5-1/4" drives for the PETs and C-64s. The difference was, I believe, >between 17 sectors on the inner tracks and 21 on the outer ones (don't quote me >on those figures). > >You could do the same thing on an optical disk, since data-storage applications >don't require constant bit-rates, the way real-time audio output does. Real-time audio output probably doesn't require constant bit-rates either. I believe that CD players read bits into a buffer asynchronously, and then put the bits out to the D-to-A at a precisely clocked rate. At least that's how I would do it. That would avoid the need for an extremely accurate drive motor. Variable bit density on the disk would only affect the rate at which program material enters the buffer. As other contributors to this discussion have noted, variable bit rates would involve some computational overhead, and it's not clear how much this would slow things down. In addition, it may be that for audio CD's the nominal bit-rate on the rotating medium is closely tuned to the bandwidth of the channel to the buffer, so that doubling the bit-rate might require some redesign. For audio applications there's no incentive for anyone to do this. (If you could double the amount of program material on a CD, do you think people would be willing to pay $30 each instead of $15? Most people think CD's are overpriced anyway.) For information storage there probably would be; if for a relatively small additional cost an optical drive could store 2Gbyte instead of 1Gbyte per platter, I'd buy that machine.. For audio applications the bucks are in selling disks; for data processing, the bucks are in selling machines. Peter S. Shenkin Columbia Univ. Biology Dept., NY, NY 10027 {philabs,rna}!cubsvax!peters cubsvax!peters@columbia.ARPA