phil@amdcad.UUCP (Phil Ngai) (11/10/86)
In article <1256@hoptoad.uucp> gnu@hoptoad.uucp (John Gilmore) writes: >I don't understand why nobody has built magnetic disks that spin at >a constant speed, but vary the clocking of data to the disk so that >all the bits end up the same width on the media. This means that you >might get 30,000 bytes per track on the inside and 90,000 on the >outside -- but who cares? On a SCSI interface, the system doesn't know >where the tracks and cylinders are anyway. See "Constant-density recording comes alive with new chips", Mark Young, _Electronic Design_, Nov 27, 1986. It shows how to solve the variable clock problem. It also talks about how it is important the disk you are using not have its own clock separator, which leaves out ESDI and SMD, with only ST506 as a acceptable commonly available drive type. Also, the drive must have a read amplifier with enough bandwidth to support the higher bit rate. Of course, if you wanted to invent your own disk this would not be a problem. And the improvement gotten from constant-density recording is on top of any RLL improvements (multiplies). Then there's the question of software. The OS now has to deal with differing number of sectors per cylinder, what would this do to the Berkeley Fast File System? Anyway, it's a good article and you should read it. -- The VT220 keyboard is an <iS<o standard. That means the French can hate it as well as the Americans. <phil <ngai +1 408 749 5720 <u<uC<p: <[ucbvax,decwrl,ihnp4,allegra<]!amdcad!phil AR<pA<; amdcad!phil@decwrl.dec.com
news@umnd-cs.UUCP (news) (11/16/86)
Question: Are there r/w heads for optical disks that can read info at higher disk speeds? And are there r/w heads that can read disks at slower speeds? Comment: If there are then why not just use two heads for r/w to the disk and keep the disk spining at the same speed? Or am I passing the technological limits of our times? I'm sure someone out there could fix that! ----------------------------------------------------------------------------- This is just an opinion not a remark. -----------------------------------------------------------------------------
bissell@rb-dc1.UUCP (jack bissell) (11/18/86)
Since one of the problems with a fast optical disk is the movement of a heavy arm and head mech. would be to not move the arm but to move the data. Yes I know the disk spins, but magnoptical disk use magnetic domains. One form of magnetic domain is a bubble memory. The next step beyound bubble is Block wall magnetic domains, where the bubble is made long and skinny, and the wall of the bubble is used to contain a 0/1 value. Thus you could just route this long skinny bubble around under the head and use the lazer to read/write on the bubble wall.