Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!pt.cs.cmu.edu!b.gp.cs.cmu.edu!Ralf.Brown@B.GP.CS.CMU.EDU From: Ralf.Brown@B.GP.CS.CMU.EDU Newsgroups: comp.sys.ibm.pc Subject: Re: RLL controllers with MFM drives Message-ID: <2542f029@ralf> Date: 23 Oct 89 11:04:09 GMT Sender: ralf@b.gp.cs.cmu.edu Organization: Carnegie Mellon University School of Computer Science Lines: 31 In-Reply-To: <4273@ncsuvx.ncsu.edu> In article <4273@ncsuvx.ncsu.edu>, unkydave@shumv1.uucp (David Bank) wrote: > Contrary to your assertion, plated media is NOT the sole >basic difference in RLL-rated drives. The biggest single difference >is in the use of VOICE COIL technology in the armature control >mechanism. This is what allows the mush more closely controlled >head movement demanded by RLL. The plated media simply makes >for a more reliable rusty pie plate. RLL *does*not* need more closely controlled head movement, since it does not change the number of cylinders on the drive. What RLL *does* need is more accurate and cleaner amplification/processing of the data stream coming off the drive. 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 1200 and 2400 bps modems. 1200 bps modems are actually 600 baud, since each change in the carrier transmits two bits of information, not just one. 2400 bps are also 600 baud, but transfer four bits of information per signal change, and thus require more accurate signal processing to recover the information from the signal changes. Unless your RLL controller magically increases the number of cylinders on the drive, it will not demand any more accurate head movement than an MFM controller for the same drive. -- UUCP: {ucbvax,harvard}!cs.cmu.edu!ralf -=-=-=-=- Voice: (412) 268-3053 (school) ARPA: ralf@cs.cmu.edu BIT: ralf%cs.cmu.edu@CMUCCVMA FIDO: Ralf Brown 1:129/46 FAX: available on request Disclaimer? I claimed something? "How to Prove It" by Dana Angluin 6. proof by omission: "The reader may easily supply the details." "The other 253 cases are analogous."