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all mfm/rll drives are rll, rll stands for run length limited iirc, if i remember right, mfm is rll 1,3 and what was called rll was rll 2,7. the main difference between the 2 is the speed/frequency (it is one or both) of the datastream. 'rll' was 50% faster and/orhigher freq it does not require any more accurate mechanism than 'mfm' it needs a read amplifier and write amplifier that can handle the datastream, i salvaged many "dead" st225's that had been run on a 'rll' controller and failed as i could remove and replace the amplifiers and add heat sinks and compound to them. then there was arll from perstore(sp) it promised 90% capacity increase on a mfm drive but was better at burning up mfm read/write amplifiers than running a mfm drive on a rll controller.
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