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Modified frequency modulation (MFM) is a run-length limited (RLL) line code [1] used to encode data on most floppy disks and some hard disk drives.It was first introduced on hard disks in 1970 with the IBM 3330 and then in floppy disk drives beginning with the IBM 53FD in 1976.
Frequency modulation encoding, or simply FM, is a method of storing data that saw widespread use in early floppy disk drives and hard disk drives. The data is modified using differential Manchester encoding when written to allow clock recovery to address timing effects known as "jitter" seen on disk media.
A modified frequency modulation, or (1,3) RLL encoding, stores each data bit as two bits on tape, but since there is guaranteed to be one 0 (no flux reversal) bit between any 1 (flux reversal) bits, then it is possible to store 6400 encoded bits per inch on the tape, or 3200 data bits per inch.
ST-506 used MFM (Modified Frequency Modulation) for the data encoding method. ST412, an ST-506 variant was available in either MFM or RLL (Run Length Limited) encoding variants. Enhanced Small Disk Interface (ESDI) was an industry standard interface similar to ST412 supporting higher data rates between the processor and the disk drive.
Modified frequency modulation (MFM) controllers were the most common type in small computers, used for both floppy disk and hard disk drives. Run length limited (RLL) controllers used data compression to increase storage capacity by about 50%. Priam created a proprietary storage algorithm that could double the disk storage.
Modified frequency modulation, a data encoding method used on floppy disks and older hard disks; Other. MFM, IATA airport code for Macau International Airport;
Differential Manchester encoding (DM) is a line code in digital frequency modulation in which data and clock signals are combined to form a single two-level self-synchronizing data stream. Each data bit is encoded by a presence or absence of signal level transition in the middle of the bit period, followed by the mandatory level transition at ...
The command data rate is 423.75 kbit/s encoded using modified frequency modulation (MFM). Tags reply to the interrogator by inductive coupling whereby the voltage across the tag antenna coil is modulated by a subcarrier. The subcarrier is derived from division of the powering field frequency.