RLL encoding

Short for Run-Length Limited encoding, RLL encoding is a method of storing information on computer hard drives, floppy disk drives, CDs, DVD, and Blu-Ray that was originally invented by IBM. This method of storage is carried out by hardware in the disk controller and is less prevalent than the modified frequency modulation (MFM) encoding scheme.

ARLL, or Advanced Run-Length Limited, is a more advanced version of RLL.