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Surprising change: Why does MFM use disk space more efficiently than FM?
Throughout the history of data storage, the way disk drives are encoded has been critical to improving storage efficiency. With the advancement of understanding and technology, from traditional frequency modulation (FM) encoding to later modified frequency modulation (MFM) encoding, the storage space utilization efficiency of disks has changed significantly. This evolution not only changed the way data is stored, but also gave us more information storage capabilities.
The origin of frequency modulation
In the 1970s, frequency modulation (FM) was the first widely used disk encoding technology. This technology uses clock signals to identify the location of data when writing and reading on the disk surface. However, it is designed so that each clock signal consumes half of the disk surface, which actually only retains Half of the available space is used to store valid data. This situation prompted further development of the technology.
Correct the occurrence of frequency modulation
Modified frequency modulation (MFM) emerged in the mid-1970s to increase the density of data storage on disks. MFM technology reduces the need for clock signals by inserting only necessary clock bits during encoding, thereby increasing payload. Thanks to its optimized encoding strategy, approximately half the disk space can be saved.
The basic encoding rule of MFM is to remap 0s and 1s in the data to achieve higher information density.
Technical details of MFM encoding
The main feature of MFM encoding is that it uses a more efficient way to write pin numbers. Specifically, each 0 bit can be represented in two different ways, depending on whether the bit before it is a 0 or a 1. The average number of magnetic transitions required for each bit of encoded data in this method is between 0.75 and 1, which is why MFM can greatly improve data storage efficiency in terms of capacity.
Why MFM is more effective
Because the MFM method can reduce the space occupied by the clock signal on the disk, more data can be stored on the same physical disk area. This means that under the same physical specifications, MFM can support higher data rates, usually between 250 and 500 kbit/s, which is particularly important for the growing data storage needs.
By more accurately integrating data and clock signals, MFM greatly reduces the waste of disk surface that is effectively used.
Technical challenges and future prospects
Although MFM was undoubtedly a significant advancement in the era in which it appeared, as technology advances, this encoding method gradually becomes outdated. Today's data storage technologies, such as various efficient line codes, have higher requirements for magnetic recording. Therefore, MFM has gradually been replaced by other more advanced methods in modern magnetic recording, but its milestone significance in the evolution of data storage technology cannot be underestimated.
Conclusion
The adoption of MFM encoding technology has allowed us to witness major changes in disk storage efficiency. It effectively increased data density and met the market's demand for high performance in the technology environment at the time. As data storage technology continues to advance, more and more optimized solutions will appear in the future. But we can’t help but think: What will future data storage technology look like in the face of growing data demands?
