Newsgroups: alt.cd-rom Path: cdrom.com!barrnet.net!sgiblab!sdd.hp.com!col.hp.com!fc.hp.com!rjn From: rjn@fc.hp.com (Bob Niland) Subject: Re: Double-sided CDs Sender: news@fc.hp.com (news daemon) Message-ID: Date: Tue, 15 Mar 1994 20:51:43 GMT Reply-To: rjn@csn.org References: <2ldhli$k5s@bigblue.oit.unc.edu> <2m2p56$cu5@pinyon.libre.com> Nntp-Posting-Host: hpfcesd.fc.hp.com Organization: Colorado SuperNet X-Newsreader: TIN [version 1.2 PL1.4] Lines: 39 Chris Goodey (goodey@pinyon.libre.com) wrote: > Laser video discs have offered double sided discs for a long time. Since 1978. > More recently double sided players have been made. Since 1988. > But you don't normally switch sides that often on a video disc, Every 30 or 60 minutes; often enough. > so perhaps they stop spinning the disc and then spin it the other way. They do indeed. Takes 15 seconds, on average. > Perhaps the drive could just read an entire track backwards and handle the > reversed data in software/firmware. This gets discussed about annually in the laserdisc & video groups. There are seriously gnarly problems with trying to do it, esp on CLV laserdiscs. It would be a little easier on CD-ROM, even though they are always CLV. > I suspect that double sided discs are just not that practical. [..on CD..] Due to the optical requirements dictating thickness of each side, a 2-sided disc has to be about 2x thick (and heavy) because virtually none have been made, and the standards don't allow for it, probably there are transports out there that would not properly servo a 2x weight platter. Since multi-platter auto-changing has been widely adopted for 120mm media, 2-sided is probably best avoided at this point. Regards, 1001-A East Harmony Road Bob Niland Suite 503 Internet: rjn@csn.org Fort Collins CompuServe: 71044,2124 Colorado 80525 USA