The ST506 interface was the first standard hard disk drive (HDD) interface used in personal computers in the early 1980s. 1 It was introduced by Seagate Technology in 1980 and used Modified Frequency Modulation (MFM) encoding to store data on the magnetic platters. 2 The ST506. Hard disk drives are accessed over one of a number of bus types, including parallel ATA (PATA, also called IDE or EIDE; described before the introduction of SATA as ATA), Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS), and Fibre Channel. Important note: On this page the connectors pinout are always given looking. MFM was not the only twin- cable hard drive interface though: aside from its close relative RLL, there was also the now long forgotten high-end competitor to SCSI, EDSI. MFM was relatively simple to implement, and quite robust. Remember that 8088 or XT based PC's ran their ISA bus at 4. It offers a balance between performance and cost-effectiveness, making it suitable for a wide range of applications.
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