Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hp-pcd!hpvcfs1!johne
From: johne@hpvcfs1.HP.COM (John Eaton)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Re: RLL controllers with MFM drives (exaggerated dangers...)
Message-ID: <670019@hpvcfs1.HP.COM>
Date: 26 Oct 89 22:18:08 GMT
References: <1989Oct23.152125.7013@Octopus.COM>
Organization: Hewlett Packard, Vancouver, WA
Lines: 17

<<<<<
< RLL and MFM both use the same number of flux
< changes per second, but RLL requires more accurate timing on the flux
< changes, since the timing carries information.
----------
This is analogous to what happened when the floppy world went from Single
density to Double density. With single density a controller would write
a 8 us pulse for a 0 and two 4 us pulses for a 1. Double density added a 
6 us pulse and was able to fit one bit in every 4 us by suitable encoding.
Note that the high and lows were the same and that they simply added a
pulse in the middle. A drive could smear a pulse by 2 us and work with
single density but could only smear by 1 us if it had to work with Double 
density.


John Eaton
!hpvcfs1!johne