Path: utzoo!mnetor!uunet!mcvax!nikhefk!henkp
From: henkp@nikhefk.UUCP (Henk Peek)
Newsgroups: comp.sys.ibm.pc
Subject: Re: What are these?  - RLL, ARLL -
Message-ID: <302@nikhefk.UUCP>
Date: 17 Jan 88 23:27:50 GMT
References: <21ecc39b@ralf.home>
Reply-To: henkp@nikhefk.UUCP (Henk Peek)
Organization: Nikhef-K, Amsterdam (the Netherlands).
Lines: 19

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