Western Digital FD1771

The FD1771, sometimes WD1771, is a

• The FD1781 was designed for
  M2FM, GCR^[3] or other double-density encodings.^[4][5]
• The FD1791-FD1797 series added internal support for
  MFM) modulation, compatible with the IBM System/34 disk format. They required an external data separator.^[6]
• The WD1761-WD1767 series were versions of the FD179x series rated for a maximum clock frequency of 1
  kbit/s for single density and 250 kbit/s for double density, thus preventing them from being used for 8-in (200 mm) floppy drives or the later "high-density" 5.25-inch (133 mm) or 90 mm floppy drives. These were sold at a lower price point and widely used in home computer
  floppy drives.
• The WD2791-WD2797 series added an internal data separator using an analog phase-locked loop, with some external passive components required for the VCO. They took a 1 MHz or 2 MHz clock and were intended for 8-inch (203 mm) and 5.25-inch (133 mm) drives.^[7]
• The WD1770, WD1772, and WD1773 added an internal digital data separator and write precompensator, eliminating the need for external passive components but raising the clock rate requirement to 8 MHz. They supported double density, despite the apparent regression of the part number, and were packaged in 28-pin DIP packages.^[8]
• The WD1772PH02-02 was a version of the chip that Atari fitted to the
  Atari STE which supported high density (500 kbit/s) operation. After production at WD could not be sustained, Atari decided to license the design and modify it to get high density and extra density (1 MBit/s) operation. The chip was codenamed "Ajax", had the number C302096 and was produced by Toshiba.^{[citation needed}
  ]

• FD179x series from SMC Microelectronics
• MB8876A and MB8877A from Fujitsu
• VL177x series from VLSI Technology.
• Soviet KR1818WG93 (КР1818ВГ93) was a WD1793 analog

These were used in many

References