Modified Frequency Modulation
Modified Frequency Modulation
Modified Frequency Modulation (MFM) is a storage encoding technique that represents digital data by varying the frequency of a carrier signal. MFM is commonly used in disk and tape drives to increase storage capacity and data transfer rates.
What does Modified Frequency Modulation mean?
Modified frequency modulation (MFM), also known as two-frequency modulation (TFM), is a type of frequency modulation (FM) used in magnetic recording. FM involves modulating the frequency of a carrier signal to represent information. In MFM, two different frequencies are used to represent the two bits of a [Binary](https://amazingalgorithms.com/definitions/binary) Code.
In conventional FM, for example, a higher frequency is used to represent a ‘1’ Bit and a lower frequency is used to represent a ‘0’ bit. In MFM, however, ‘0’ bits are represented by no modulation (i.e., the carrier frequency), while ‘1’ bits are represented by a frequency modulation. This has the advantage of reducing the bandwidth required to transmit the same amount of information (a ‘1’ bit still takes up more bandwidth than a ‘0’ bit, but both take less bandwidth than in conventional FM), because the carrier frequency is not used to represent data.
Applications
MFM is primarily used in magnetic recording, such as hard disk drives (HDDs) and Floppy Disk drives (FDDs). It is also used in floppy tape and Cassette tape drives. MFM is well-suited for these applications because it offers a good compromise between bandwidth and data density. It is more bandwidth-efficient than conventional FM, but it can still achieve high data densities.
One notable application of MFM is in the Enhanced Small Device Interface (ESDI) standard for hard disk drives. ESDI uses MFM to achieve data transfer rates of up to 20 Mbit/s, which was a significant improvement over the earlier ST-506 standard.
History
MFM was introduced by IBM in 1979. It was developed as an improvement over conventional FM to reduce bandwidth requirements while maintaining high data densities. MFM quickly became the standard for magnetic recording in the 1980s and 1990s. However, as the demand for higher data densities increased, MFM was eventually replaced by more advanced modulation schemes, such as Run-Length Limited (RLL) and Partial Response Maximum Likelihood (PRML).