The FD1771, sometimes WD1771, is a

floppy disk controller A floppy-disk controller (FDC) is a hardware component that directs and controls reading from and writing to a computer's floppy disk drive (FDD). It has evolved from a discrete set of components on one or more circuit boards to a special-purpo ...

chip, the first in a line of floppy disk controllers produced by

Western Digital Western Digital Corporation is an American data storage company headquartered in San Jose, California. Established in 1970, the company is one of the world's largest manufacturers of hard disk drives (HDDs). History 1970s Western Digital ...

. It uses single density FM encoding introduced in the IBM 3740. Later models in the series added support for MFM encoding and increasingly added onboard circuitry that formerly had to be implemented in external components. Originally packaged as 40-pin

dual in-line package In microelectronics, a dual in-line package (DIP or DIL) is an Semiconductor package, electronic component package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be through-hole technology, throu ...

(DIP) format,"The FD1771 is a single-chip floppy disk formatter/controller that interfaces with most available disk drives and virtually all types of computers." The FD1771 was announced on July 19, 1976, and sold for $60 each in lots of 100. later models moved to a 28-pin format that further lowered implementation costs.

Derivatives

The FD1771 was succeeded by many derivatives that were mostly software-compatible: *The FD1781 was designed for

double density Disk density is a capacity designation on magnetic storage, usually floppy disks. Each designation describes a set of characteristics that can affect the areal density of a disk or the efficiency of the encoded data. Such characteristics includ ...

, but required external modulation and demodulation circuitry, so it could support MFM, M2FM,

GCR GCR (or GCRS) may refer to: Science * Galactic cosmic ray, a cosmic ray from outside the Solar System * Geocentric Celestial Reference System, a coordinate system for near-Earth objects like satellites * Geological Conservation Review, a procedu ...

or other double-density encodings. The FD1781 was announced on September 21, 1977. Supported Dual density; accommodates MFM, M2FM. *The FD1791-FD1797 series added internal support for

( MFM) modulation, compatible with the IBM System/34 disk format. They required an external data separator.FD 179X-02 datasheet
/ref> *The WD1761-WD1767 series were versions of the FD179x series rated for a maximum clock frequency of 1

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base u ...

, resulting in a data rate limit of 125

kbit/s In telecommunications, data transfer rate is the average number of bits ( bitrate), characters or symbols ( baudrate), or data blocks per unit time passing through a communication link in a data-transmission system. Common data rate units are mu ...

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" or 90 mm floppy drives. These were sold at a lower price point and widely used in

home computer Home computers were a class of microcomputers that entered the market in 1977 and became common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a s ...

floppy drives. *The WD2791-WD2797 series added an internal data separator using an analog

phase-locked loop A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is fixed relative to the phase of an input signal. Keeping the input and output phase in lockstep also implies keeping the input and ou ...

, with some external passive components required for the VCO. They took a 1 MHz or 2 MHz clock and were intended for and drives. *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.WD177X-00 datasheet images
/ref> *The WD1772PH02-02 was a version of the chip that Atari fitted to the

Atari STE Atari ST is a line of personal computers from Atari Corporation and the successor to the company's Atari 8-bit computers, 8-bit computers. The initial model, the Atari 520ST, had limited release in April–June 1985, and was widely available i ...

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.

Compatible chips

Many compatible chips were available from other vendors: *FD179x series from SMC Microelectronics *MB8876A and MB8877A from Fujitsu *VL177x series from

VLSI Technology VLSI Technology, Inc., was an American company that designed and manufactured custom and semi-custom integrated circuits (ICs). The company was based in Silicon Valley, with headquarters at 1109 McKay Drive in San Jose. Along with LSI Logi ...

. *Soviet KR1818WG93 (КР1818ВГ93) was a WD1793 analog These were used in many

microcomputer A microcomputer is a small, relatively inexpensive computer having a central processing unit (CPU) made out of a microprocessor. The computer also includes memory and input/output (I/O) circuitry together mounted on a printed circuit board (P ...

s including the

TRS-80 The TRS-80 Micro Computer System (TRS-80, later renamed the Model I to distinguish it from successors) is a desktop microcomputer developed by American company Tandy Corporation and sold through their Radio Shack stores. Launched in 1977, it is ...

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BBC Master The BBC Master is a home computer released by Acorn Computers in early 1986. It was designed and built for the BBC, British Broadcasting Corporation (BBC) and was the successor to the BBC Micro, BBC Micro Model B. The Master 128 remained in prod ...

Atari ST Atari ST is a line of personal computers from Atari Corporation and the successor to the company's Atari 8-bit computers, 8-bit computers. The initial model, the Atari 520ST, had limited release in April–June 1985, and was widely available i ...

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, and the SAM Coupé, as well as the +D and DISCiPLE disk interfaces for the

ZX Spectrum The ZX Spectrum () is an 8-bit computing, 8-bit home computer developed and marketed by Sinclair Research. One of the most influential computers ever made and one of the all-time bestselling British computers, over five million units were sold. ...

, the Commodore 157x/ 1581 for the

Commodore 64 The Commodore 64, also known as the C64, is an 8-bit computing, 8-bit home computer introduced in January 1982 by Commodore International (first shown at the Consumer Electronics Show, January 7–10, 1982, in Las Vegas). It has been listed in ...

and the

Atari XF551 The XF551 is a 5 1/4 inch floppy disk drive produced by Atari, Inc. for the Atari 8-bit computers. Introduced in 1987, it matches the gray design language of the XE models. It was the first drive from the company with official support for double ...

for the

Atari 8-bit computers The Atari 8-bit computers, formally launched as the Atari Home Computer System, are a series of home computers introduced by Atari, Inc., in 1979 with the Atari 400 and Atari 800. The architecture is designed around the 8-bit MOS Technology 650 ...

Derivatives

Compatible chips

References

Further reading