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Definition: RLL

(Run Length Limited) An encoding method commonly used on magnetic disks, including RLL, IDE, SCSI, ESDI, SMD and IPI interfaces. The actual number of bits recorded on the disk is greater 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 improve, fewer extra bits are inserted, and the ratio of data bits to recorded bits becomes 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.