The disk controller is the electronic assemblage that governs the mechanics of a a hard drive, floppy disk or other kind of disk drive. Its role is to control the rotating spindle, the position of the heads for reading and writing and interpret the electrical signals received to convert them into data in a particular location on the surface of the hard drive. Early disk controllers were identified by their storage methods and data encoding, typically implemented on a separate controller card. 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%.
The most common interface provided nowadays by disk controllers are PATA (IDE) and Serial ATA for home use. High-end disks use SCSI, Fibre Channel or Serial Attached SCSI. Disk controllers can also control the timing of access to flash memory which is not mechanical in nature (i.e. no physical disk).
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