Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!cica!sol.ctr.columbia.edu!samsung!uunet!crdgw1!sixhub!davidsen From: davidsen@sixhub.UUCP (Wm E. Davidsen Jr) Newsgroups: comp.sys.ibm.pc Subject: Re: Here we go again: was Re: MFM on RLL? Keywords: read the Monthly Frequently Asked Questions Message-ID: <641@sixhub.UUCP> Date: 17 Mar 90 21:28:34 GMT References: <2881@uwm.edu> <3087@jato.Jpl.Nasa.Gov> Reply-To: davidsen@sixhub.UUCP (bill davidsen) Distribution: comp Organization: *IX Public Access UNIX, Schenectady NY Lines: 35 In article <3087@jato.Jpl.Nasa.Gov> kaleb@mars.UUCP (Kaleb Keithley) writes: | RLL is *NOT* tougher on a drive than MFM. RLL uses a different encoding | scheme to achieve a higher *data* density, however the physical bit density | on the platters is exactly the same. Well, not exactly. Actually standard MFM is really "RLL 1,3" while most people mean "RLL 2,7" when they say RLL. The first number is the *closest* spacing between flux changes on the media in terms of the data clock rate, while the second is the *greatest* distance. Now even with the data clock running 50% faster, the MFM controller actually puts the flux changes closer together than the RLL. The problem is the second number. Since the RLL controller is waiting a longer period between pulses, the accuracy of rotational speed (usually good) and the read amplifiers (frequently not so good) determines if a drive will work RLL or not. I have yet to see any rational explanation of damage to a drive done by running RLL. I am assurred that the MFM and RLL rated drives from most manufacturers are made on the same lines, and the RLL drives are just tested better. The reason they are not rated RLL may be (a) because they weren't tested, and the manufacturer doesn't want to eat one on warantee if it will run MFM but not RLL, or (b) because it was tested and failed. (a) is more likely, and therefore (read this carefully) most MFM drives for which there is a matching RLL version will run RLL. Of course you have no comeback if the drive won't run RLL, but I have had very good luck with recent Seagates, Priams, etc. I have had some bad luck with Maxtor, which surprised me, and which may not be typical. -- bill davidsen - davidsen@sixhub.uucp (uunet!crdgw1!sixhub!davidsen) sysop *IX BBS and Public Access UNIX moderator of comp.binaries.ibm.pc "Getting old is bad, but it beats the hell out of the alternative" -anon