RLL-RUN LENGTH LIMITED COMPRESSION
Run Length Limited (RLL) Compression is a data compression technique widely used in hardware data storage/transmission. The idea is to translate binary data into codes that avoid cases that would otherwise limit storage densities and/or transmission speeds. This is useful when, for example, the size/duration of a storage block ('bit') can be measured very accurately, but the time to transition between states is comparatively slow. The resulting codes are somewhat longer than the original, but can be stored more densely or transmitted at higher rates than the original data. For example, magnetically stored data is often stored using a 2,7 RLL scheme that avoids storing one bits too closely together. 2,7 RLL guarantees that at least 2 and no more than 7 0s will appear between each encoded 1. The enforced separation of 1 bits allows storage densities that yield an overall 50% increase in storage capacity above straight binary storage.
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Copyright 1994-2002 by Donald Kenney.