ELORANTA@BRANDEIS.BITNET (01/05/87)
IBM drives are using double denstity and apple is using single
density. So IBM could read apple disks (with special program) and apple can't
read IBM (normal standard) disks.
I don't know if it is possible to make single density disks with IBM but
if it can then apple might be able to read those single density disks.
Jussi Eloranta.darrelj@sdcrdcf.UUCP (Darrel VanBuer) (01/07/87)
In article <8701051528.aa00868@SPARK.BRL.ARPA> ELORANTA@BRANDEIS.BITNET writes: > > IBM drives are using double denstity and apple is using single density. ^^^^^^^^^^^^ > So IBM could read apple disks (with special program) and apple can't > read IBM (normal standard) disks. > Jussi Eloranta. No, no no!!! Apple Disks use their own, unique 1.5 density recording scheme which no "standard" disk controllers can do anything with. With some real grungy assembly language programming, an Apple controller could do single density because it has the ability to selectively write both clock and data pulses on the disk. Double density is impossible because some pulses have to be written halfway between normal pulse positions, and some have to be shifted about 12% either way to compensate for bit shift on the media. (There may be complications in Apple reads of single density; I don't know if missing clock timing schemes for standard FM are sufficiently compatible with the Apple controller hardware state machine which sets initial syncronization with the incoming data. The remainder of the hardware is two 8-bit shift registers so that software can (must) do just about anything at the bit level on the disk. -- Darrel J. Van Buer, PhD System Development Corp. 2525 Colorado Ave Santa Monica, CA 90406 (213)820-4111 x5449 ...{allegra,burdvax,cbosgd,hplabs,ihnp4,orstcs,sdcsvax,ucla-cs,akgua} !sdcrdcf!darrelj darrel@sdc-camarillo.ARPA or VANBUER@USC-ECL.ARPA