henkp@nikhefk.UUCP (Henk Peek) (01/18/88)
In article <21ecc39b@ralf.home> Ralf.Brown@B.GP.CS.CMU.EDU writes: }In article <675@bucket.UUCP>, leonard@bucket.UUCP (Leonard Erickson) writes: }}Single density disks (which do exist in 5.25!) use FM recording. This is }}data-bit clock-bit data-bit..... }} }}Double density disks (and QD & HD & "normal" hard disks) use MFM. This }}uses some sort of scheme (I forget the details) to make the data }}"self-clocking" and thus eliminate the clock-bits. This enabled twice }}the data density, thus the term double-density. }MFM is really RLL 1,3 (i.e. at most 3 zero or one bits in a row). The RLL MFM is really RLL 2,3 (there must at last 2 half bit cels with the same value) }controllers use RLL 2,7 (at most 7 identical bits in a row), and ARLL uses }(I think) RLL 3,9. They are using mostly ARLL 1.7 Henk Peek ..!uunet!mcvax!nikhefk!henkp.UUCP