On Fri, 27 Aug 1999, COPLIN, Nicholas. wrote: > along similar lines to this thought, it could be an issue similar to that > with 1581 disks, but more correctly: the issue is magnetic flux density, > etc. or even more correctly "oersted of magnetic coercivity". > > lower density disks have lower values, and higher density disks higher > values. I don't specifically know anything about the 8280, but the ability > to write is heirachial: if it is SD (single density) then only SD disk will > do. if it is DD, then SD or DD disks will work, but the SD disks may not be > readable in another SD only drive, etc for HD.... You can tell if its SS or > DS by checking the heads, but at worst case you'll only have a half formated > disk.... (did the 8inch disk you have say "SSSD of DSDD, ... if they are > pre-formatted and of higher density than the drive you may not generate the > "oerstads" to overwrite Close. The magnetic coercivity is a property of the chemical composition of the particles making up the magnetic film on the disk. It is a measure of the energy required to change the magnetic field of the particles. Single Density (SD), Double Density (DD), or Quad Density (QD) is a function of the size of the magnetic domains of the magnetic particles. SD, DD, and QD disks have magnetic particles with the same coercivity. Supposedly, the only difference is the size of the magnetic particles, and thus, the size of the magnetic domains. In practice, no one makes the SD particles any more. Disks are all made from particles that can do QD or better. HD disks have the same capacity as QD disks, but they have a different coercivity. Most 3.5" drives have electronic circuitry to write correctly to the higher coercivity of HD disks, but can switch to a mode that will also write correctly to the lower coercivity of DD disks. 5.25" and 8" drives do not do this. Judging from the number of the 8280 drive, it should be analogous to the 8250 drive, that is Double sided Quad Density (DSQD). Almost nobody uses QD disks in an 8250. DSDD disks work just fine. Another problem arises if the disk is already formatted in an incompatible format. In that case, formatting a track may not completely erase the existing format. Reading the track may then result in reading the new track and the remainig part of the old track at the same time, thus causing a read error. The fix is easy. Bulk erase the disks with a bulk tape eraser. -------------------------------- I have been trying to determine which drive mechanisms (manufacturer and model number) were used in the various Commodore drives. I do not have information on what drive mechanism the 8280 drive uses. You obviously have one. Could you provide that information.? - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail cbm-hackers-request@dot.tcm.hut.fi.
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