The disk controller (or "hard disk controller") is the circuit which allows the CPU to communicate with a hard disk, floppy disk or other kind of disk drive.

Early disk controllers were identified by their storage methods and data encoding. They were 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%. Priam created a proprietary storage algorithm that could double the disk storage. Shugart Associates Systems Interface, (SASI) was a predecessor to SCSI.