Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!olivea!tymix!cirrusl!ss168!dhesi From: dhesi%cirrusl@oliveb.ATC.olivetti.com (Rahul Dhesi) Newsgroups: comp.unix.sysv386 Subject: Re: Does ESIX still not support RLL? Message-ID: <3087@cirrusl.UUCP> Date: 24 Apr 91 18:45:08 GMT References: <1991Apr21.155642.1586@shambala.uucp> <1991Apr22.210543.27730@thyme.jpl.nasa.gov> <3080@cirrusl.UUCP> <513@pyrite.nj.pyramid.com> Sender: news@cirrusl.UUCP Reply-To: Rahul Dhesi Lines: 47 I wrote: How can ESIX even know whether the controller uses RLL? How can anybody find this out without ripping the disk apart and analyzing the bit-patterns stored on the platter? Bill Pechter writes: If there's more than the standard number of MFM sectors per track -- you lose. RLL does 25, ERLL (Perstor) does 31... So if the driver expects 1-17 only... you may not see your full disk sizes (at best). Which sort of answers the question, but not really. There is no such thing as "the standard number of MFM sectors per track." Perhaps there is such a thing as "many disk drives use 17 sectors per track, and many more don't." The following is directed not towards Bill, but towards many Usenet users who assume that RLL is some sort of disk interface standard. It's not! It's just a way of putting bit patterns on the disk surface. And it wasn't invented by Adaptec either. RLL means "run length limited" -- a way of recording bits such that you never have more than m consecutive raw ones or n consecutive raw zeroes. Tape drives have used it for years (but they call it GCR or group code recording). In the microcomputer world, the Apple II used it on floppy disks way back when. I still don't see how ESIX (or any other operating system) can find out whether the the controller uses RLL. I can see that an operating system might not support a certain number of sectors per track, but that has only a very nebulous relationship to the recording format used, other than that formats denser than MFM yield more sectors per track. Perhaps Usenet posters ought to be saying "ESIX requires no more than 17 sectors per track" (if that is true, which it probably is not, because the disk off which I run ESIX has more than 17 sectors per track) instead of blaming it on the recording format. Better, still, say something like "ESIX doesn't support my disk controller, and it happens to use RLL recording, but the recording format many or many not have something to do with it." -- Rahul Dhesi UUCP: oliveb!cirrusl!dhesi