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Definition: RLL


(Run Length Limited) The encoding method commonly used on magnetic disks, including SATA, SAS, PATA and SCSI interfaces. There are more bits recorded on the disk than the data bits. Earlier drives inserted extra bits into the data stream so there was more space between signals when reading the data back. As electronics improved, fewer extra bits were inserted, and the ratio of data bits to recorded bits became greater.

The "run length" is the number of consecutive 0s before a 1 bit is recorded. For example, RLL 1,7 means there must be at least one 0 between every 1, and the 7 means a maximum of eight time periods between flux transitions. See hard disk interfaces and hard disk.