Floppy-disk controller

Early controllers required additional circuitry to perform specific tasks like providing clock signals and setting various options.

Later designs included more of this functionality on the controller and reduced the complexity of the external circuitry; single-chip solutions were common by the later 1980s.

In these systems, the controller also often combined a microcontroller to handle data transfer over standardized connectors like SCSI and IDE that could be used with any computer.

IBM's 1973 introduction of the 3740 Data Entry System created the basic media standard for the 8-inch single sided floppy disk, IBM's "Type 1" diskette, which coupled with rapidly increasing requirements for inexpensive, removable direct access storage for many small applications caused a dramatic growth in drive and controller shipments.

[4] Examples of such FDCs include: The first FDC implemented as a special purpose integrated circuit is the Western Digital FD1771[14] announced on 19 July 1976.

[17] The μPD765 became a quasi-industry standard when it was adopted in the original IBM PC (1981); the FDC was physically located on its own adapter card along with support circuitry.

[19] In early 1987, Intel introduced the 82072 CHMOS High Integrated Floppy Disk Controller for use in industry standard PC computers.

One of the functions of the controller is to turn the original data into the proper pattern of polarizations during writing, and then recreate it during reads.

In some systems, like the Apple II and IBM PC, this is controlled by software running on the computer's host microprocessor and the drive interface is connected directly to the processor using an expansion card.

On other systems, like the Commodore 64 and Atari 8-bit computers, there is no direct path from the controller to the host CPU and a second processor like the MOS 6507 or Zilog Z80 is used inside the drive for this purpose.

This allowed Apple to arrange a deal with Shugart Associates for a simplified drive that lacked most of its normal circuitry.

An alternative arrangement that is more usual in recent designs has the FDC included in a super I/O chip which communicates via a Low Pin Count (LPC) bus.

[25] In the IBM PC family and compatibles, a twist in the cable is used to distinguish disk drives by the socket to which they are connected.