MFM meaning in Information Technology ?

Modified frequency modulation (MFM) is a run-length limited (RLL) line code used to encode data on most floppy disks. It was first introduced in hard disk drives in 1970 with the IBM 3330 and then in floppy disk drives beginning with the IBM 53FD in 1976.

MFM is a modification to the original frequency modulation (FM) code. Due to the minimum spacing between flux transitions that is a property of the disk, head and channel design, MFM, which guarantees at most one flux transition per data bit, can be written at higher density than FM, which can require two transitions per data bit.

MFM is used with a data rate of 250–500 kbit/s (500–1000 kbit/s encoded) on industry-standard 5+1⁄4-inch and 3+1⁄2-inch ordinary and high-density floppy diskettes. MFM was also used in early hard disk designs, before the advent of more efficient types of RLL codes. Outside of niche applications, MFM encoding is obsolete in magnetic recording.