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The Art of Data Storage: How did early disk drives design efficient MFM encoding?
With the rapid development of digital technology, the way data is stored has also undergone many changes. In this process, improved frequency modulation (MFM) encoding technology played a crucial role in the evolution of disk drives. Since the IBM 3330 hard drive first adopted MFM technology in 1970, this encoding scheme has quickly gained widespread use due to its efficiency and stability. This article will explore the design principles of MFM encoding and its impact on disk drives.
Basics of magnetic storage technology
Magnetic storage devices, such as hard drives and tapes, do not store data in absolute terms like other types of storage media, but instead rely on changes in magnetic poles. When the magnetic field changes, it induces current in nearby wires and vice versa. By sending a series of changing currents to the read-write head, when the media moves, a series of magnetic pole patterns will be formed on the media. The changes in these patterns represent data "1"s.
This technology allows disk drives to efficiently encode and decode data on storage media, resulting in higher data transfer rates.
The birth of frequency modulation coding
Frequency modulation encoding (FM) is an encoding system commonly used in early disk drives. The FM-encoded driver controller contains a precise clock signal that operates at half the selected data rate. As data is written to the disk, the clock signal is interleaved with the data so that when it is read, the clock signal is used as a short-term trigger to indicate the presence or absence of a data bit.
MFM encoding: a revolution in improving storage density
MFM encoding innovatively integrates the encoding of clock signals and data in a "clock window". Unlike FM, clock bits are only written when needed to maintain synchronization, thus achieving twice the information density of FM on average. The MFM encoding rules determine the output format of 0s and 1s, optimizing the number rate of magnetic conversion and reducing the possibility of data errors.
This technique not only improved data storage capacity, but also opened up new process possibilities for hard drive design at the time.
The Art of Data Splitter
MFM systems require a more precise clock signal, so integrating the required analog and digital components into a single integrated circuit was not economical at the technology level of the late 1970s. This drove the development of a system called a data splitter. Data splitter design is an art, and one of the most widely used controllers is the Western Digital FD1771 series. This series of hardware plays an important role in promoting the popularity of MFM encoding.
Data formatting and row encoding
The application of FM and MFM technology aims to indicate the location of each bit in the original data, but the data itself does not have a higher-level organizational form, such as a "file". Disks are usually formatted as fixed-size sectors, which contain additional header information to link them back to the file. Such a structural design ensures efficient management of data and improves the efficiency of data reading.
Backwards Compatibility and Evolving MFM
Although the improved frequency modulation encoding (MMFM) simplifies the original MFM format, its importance gradually diminishes in the face of new data storage technology challenges. However, MFM still occupies a place in many current technical discussions of data storage systems, becoming a key technology for understanding the development of early disk drives.
Although MFM encoding is considered obsolete in current magnetic recording, it undoubtedly paved the way for later data storage technologies.
When we look back on this period of history, the design of MFM coding is not only a technological breakthrough, but also a profound reflection on data management and efficiency thinking. Where will today's data storage technology go?
