On Wed, 12 Aug 2015 13:21:45 -0500, Joel Ewing wrote: > My strong impression was that the erased IBG between physical blocks was a >requirement for proper sensing of beginning of a block. The requirement >that some 32-byte increments must be left unused for IBGs indicates >these 32-byte groupings do not play the same role as fixed data blocks >in FBA architecture devices. > "left unused"? or marked as unused? (although this may be a distinction without a difference). And it may depend on choice of encoding technique: NRZI? MFM? GCR: (0,2) RLL? The last is interesting because it has 17 encodings available to represent a 4-bit nybble. Some systems use the extra code point to signal control information, which might be a logical IBG.
https://en.wikipedia.org/wiki/Run-length_limited#GCR:_.280.2C2.29_RLL -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN