In message , at
23:48:40 on Thu, 24 Jun 2010, John Rumm
remarked:
RLL Compression? Pray tell me more.

Run length limiting. Using a RLL controller gained an extra 50%
capacity, but at the expense of a reduced signal to noise and grater
risk of unrecoverable read error.

Other way round, surely? It was a coding method to make sure you never
had too many of the same polarity bits "in a row", which risks
unreadability. What makes a magnetic storage medium work is *changes* in
polarity.
--
Roland Perry