Run-length Limited - History

History

All codes used to record on magnetic disks have limited the run of zero transitions and can therefore be characterized as RLL codes. The earliest and simplest variants were given specific names, such as Modified Frequency Modulation (MFM); often, "RLL" refers only to the more complex variants not given such specific names, but that is technically incorrect.

The RLL terminology in hard disk drive art, specifically RLL (2,7), was originally developed by IBM engineers, and was first used commercially in 1979 on the IBM 3370 DASD, for use with the 4300 series mainframe. During the late 1980s, PC hard disks began using RLL proper (i.e. variants more complex than those that had received their own proper names, such as MFM). RLL codes have found almost universal application in optical disc recording practice since 1980. In consumer electronics, RLLs like the EFM code with (Eight-to-Fourteen:rate = 8/14, d=2, k=10) are employed in the Compact Disc (CD) and MiniDisc (MD), and the EFMPlus code (rate = 8/16, d=2, k=10) used in the DVD. Parameters d, k are the minimum and maximum allowed run-lengths. For more coverage on the storage technologies, the references cited in this article are useful.