Western Digital FD1771
First Western Digital floppy disk controller chip.
The FD1771, sometimes WD1771, is a floppy disk controller chip and the first in a line of floppy disk controllers produced by Western Digital. It uses single density FM encoding introduced in the IBM 3740. Originally packaged as a 40-pin dual in-line package (DIP) format, it set the foundation for a series of derivatives that added support for double density encoding and increasingly integrated onboard circuitry.
- Manufacturer
- Western Digital
- Encoding
- single density FM (IBM 3740)
- Package
- 40-pin DIP
- Also known as
- WD1771
Lore & Background
The FD1771 was the inaugural chip in Western Digital's floppy disk controller line, employing single density FM encoding as introduced in the IBM 3740. It was packaged in a 40-pin dual in-line package (DIP) format. Later models in the series added support for MFM encoding and increasingly incorporated onboard circuitry that formerly required external components, eventually moving to a 28-pin DIP format to lower implementation costs.
The FD1771 was succeeded by many software-compatible derivatives. These included the FD1781 for double density with external modulation/demodulation circuitry, the FD1791-FD1797 series with internal MFM support but requiring an external data separator, and the WD1761-WD1767 series rated for lower clock frequencies. The WD2791-WD2797 series added an internal analog phase-locked loop data separator, while the WD1770, WD1772, and WD1773 introduced an internal digital data separator and write precompensator, eliminating external passive components.
Compatible chips from other vendors included the FD179x series from SMC Microelectronics, MB8876A and MB8877A from Fujitsu, VL177x series from VLSI Technology, and the Soviet KR1818WG93 (КР1818ВГ93) as a WD1793 analog. These chips were used in many microcomputers such as the TRS-80, Acorn Electron, BBC Master, Atari ST, Acorn Archimedes, and SAM Coupé, as well as disk interfaces for the ZX Spectrum, Commodore 64, and Atari 8-bit computers.
Reader's Guide
The FD1771 established the foundational architecture for Western Digital's floppy disk controller family, which became widely adopted across home and personal computers. Its single density FM encoding, derived from the IBM 3740, set a standard that later derivatives expanded upon with double density MFM support and integrated circuitry. The chip's 40-pin DIP package and the subsequent shift to 28-pin packages reflected ongoing cost reduction efforts. The extensive line of software-compatible derivatives—from the FD1781 to the WD1770 series—allowed manufacturers to choose appropriate levels of integration and performance for their systems. The availability of compatible chips from multiple vendors, including SMC Microelectronics, Fujitsu, VLSI Technology, and Soviet manufacturers, further cemented the FD1771's influence. Its legacy is evident in the wide range of microcomputers and disk interfaces that employed these controllers, from the TRS-80 and Acorn machines to Atari and Commodore systems. The FD1771's design principles and the ecosystem it spawned shaped the floppy disk controller market for years, with later models like the WD1772PH02-02 supporting high density operation and even extra density through licensed derivatives such as the Toshiba-produced 'Ajax' chip.
Did You Know?
- The WD1772PH02-02 was a version fitted to the Atari STE that supported high density (500 kbit/s) operation.
- The Soviet KR1818WG93 (КР1818ВГ93) was a compatible analog of the WD1793.
Frequently Asked Questions
What is the Western Digital FD1771?
The FD1771 (also called the WD1771) is a floppy disk controller chip designed and manufactured by Western Digital. It holds the distinction of being the very first floppy disk controller the company ever produced.
What encoding scheme does the FD1771 support?
It handles single density FM encoding, the same format originally defined for the IBM 3740 drive. Notably, it does not natively support double density encoding on its own.
What physical package does the FD1771 come in?
The chip is housed in a 40-pin dual in-line package (DIP), a relatively large footprint even for its era. That DIP form factor was standard for the era's discrete controller ICs.
Why do storage-history fans care about the FD1771?
It is the foundational chip in Western Digital's entire floppy controller lineage, and every later derivative built on the groundwork it established. Without it, the subsequent double-density and highly integrated successors simply would not have existed.
What happened to the FD1771 after it was released?
Western Digital followed it with a series of derivative chips that added double density support and progressively more onboard circuitry. The original FD1771's role as the baseline single-density controller was effectively handed off to those more capable follow-ups.
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