CompuServe Messages

RLL gets higher DATA density with the same number of flux changes. It does this by eliminating the need for a continuous clock signal. Since you need to sync off of SOMETHING, the data is restructured such that there are always enough flux reversals to substitute for the missing clock signal. This is done by substituting specific flux reversal patterns for the bit patterns such that there is a minimum and maximum number of successive zeros and ones; thus the name RLL: the full name of the standard scheme is Run Length Limited 2,7 (the 2 and 7 referring to limits on successive flux reversals). Since this is more demanding of the media, MFM drives will generally not be reliable storing RLL data. Media type is therefore _indirectly_ connected with RLL, but it's not primary to the issue of how the data density is increased. The key point to remember: the DATA density is increased; the FLUX density doesn't change. We discussed this a few months ago here. I can dig up my references and type in the specifics again if you need the information? Rick