On Tue, Jul 10, 2001 at 02:23:42PM -0400, David Douthitt wrote: > "Michael H. Warfield" wrote: > > Typically, for "rotating magnetic" (hard drives, floppies, etc) > > and others with concentric tracks, track zero starts on the outside and > > increasing tracks progress toward the center. These are also your > > "constant angular velocity" drives and the outer tracks have the highest > > head to media velocity and, consequently, the best signal to noise > > ratio. > > CD Roms and DVDs are actually "constant linear velocity" drives > > and utilize a single spiral track which starts at the hub and progresses > > outward. That's why you can have "mini" CDs and "Business Card" CDs, > > because the drive, in this case, starts and the hub, which is at the same > > location for all of them, and spirals outward. > My understanding is that the original Mac 3.5" floppy drive (and later, > the Apple II SuperDrive) were all variable-speed; out of curousity.... > how was it with them, and how did the variable speed affect the layout > of the tracks? I couldn't say if they were "constant linear velocity" > but one suspects they must have been... Now that one, I really can't answer. I use to work on the old "hard sectored" floppies back in the bad old days and they were also track zero on the outside rim. They had a physical "track zero switch" that had to be adjusted when calibrating the drive. Those were all CAV drives. I don't know if the the old Apple drives were CLV drives or not, but I would STRONGLY suspect that they were all track zero on the outer rim. I would suspect that JUST because all of those drives (8", 5-1/4", and 3-1/2") all had track zero sensors (switches or optical) on the outer reaches of the head movement on the drive frames. I never saw one with a limit detector near the hub. IIRC... There were also some floppy drives (or flippy drives, or some off the wall variation) that was neither CAV or CLV. They were "zoned". Within each "zone" they were CAV and had a fixed number of sectors per track. But there were two or more zones per disk and each zone operated with a different number of sectors (and possible a different rotational speed). I know the ancient IOMEGA "Take 10" 10 Meg 5-1/4 floppies worked this way. Again, IIRC... I believe that the Take 10 drives had two zones with different numbers of sectors per track in each zone. I also believe (but I'm not quite as sure) that the speed changed between the two zones to improve the SNR in the inner zone. Some "Bernolli box" floppies might have also worked this way. All of them had track zero on the outer track, however. That much WAS consistant with everything in my experience, other than the CDs and DVDs. > Also, how is it the miniCDs are not round? The true miniCDs ARE round. BC CD's are not round but they are mini CD's that are cut (or molded) so the flat edges are BC (business card) sized. You can get round miniCDs that hold about 100 - 150 Meg. The BC shaped miniCDs only hold about 45 - 50 Meg. Their track ends at the point where it conflict with the square edge shaping, not where the normal miniCD limit is at. A stack of BC CD-Rs I bought don't even have the aluminized layers out past the fully circular area in the middle. The "wings" (the area past the squared off molding) are clear through. The rounded "wings" are there to insure that the center correctly into the miniCD depression on the CD drive trays. Mike -- Michael H. Warfield | (770) 985-6132 | mhwat_private (The Mad Wizard) | (678) 463-0932 | http://www.wittsend.com/mhw/ NIC whois: MHW9 | An optimist believes we live in the best of all PGP Key: 0xDF1DD471 | possible worlds. A pessimist is sure of it! ----------------------------------------------------------------- This list is provided by the SecurityFocus ARIS analyzer service. For more information on this free incident handling, management and tracking system please see: http://aris.securityfocus.com
This archive was generated by hypermail 2b30 : Thu Jul 12 2001 - 11:05:09 PDT