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Western Digital FD1771
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<h2 id="derivatives">Derivatives</h2> <p>The FD1771 was succeeded by many derivatives that were mostly software-compatible: </p> <ul><li>The FD1781 was designed for <a href="/facts/Double_density/S4YBgHjD">double density</a>, but required external modulation and demodulation circuitry, so it could support <a href="/facts/Modified_Frequency_Modulation/XLIItN1f">MFM</a>, <a href="/facts/M2FM/XLIItN1f">M2FM</a>, <a href="/facts/Group_coded_recording/rz5tW8Jq">GCR</a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> or other double-density encodings.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a><a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a></li> <li>The FD1791-FD1797 series added internal support for <a href="/facts/Double_density/S4YBgHjD">double density</a> (<a href="/facts/Modified_Frequency_Modulation/XLIItN1f">MFM</a>) modulation, compatible with the <a href="/facts/IBM_System/34/N1wT4qp8">IBM System/34</a> disk format. They required an external data separator.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a></li> <li>The WD1761-WD1767 series were versions of the FD179x series rated for a maximum clock frequency of 1 <a href="/facts/MHz/6Wshj5qm">MHz</a>, resulting in a data rate limit of 125 <a href="/facts/Kbit/s/Nv9VoT7T">kbit/s</a> 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 <a href="/facts/Home_computer/CDEPVd1T">home computer</a> floppy drives.</li> <li>The WD2791-WD2797 series added an internal data separator using an analog <a href="/facts/Phase-locked_loop/sgmca8aQ">phase-locked loop</a>, with some external passive components required for the <a href="/facts/Voltage-controlled_oscillator/85sdYF0m">VCO</a>. They took a 1 MHz or 2 MHz clock and were intended for 8-inch (203 mm) and 5.25-inch (133 mm) drives.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a></li> <li>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.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a></li> <li>The WD1772PH02-02 was a version of the chip that Atari fitted to the <a href="/facts/Atari_STE/9GsYSlaM">Atari STE</a> 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.</li></ul> <h2 id="compatible-chips">Compatible chips</h2> <p>Many compatible chips were available from other vendors: </p> <ul><li>FD179x series from SMC Microelectronics</li> <li>MB8876A and MB8877A from <a href="/facts/Fujitsu/6e5gvNSa">Fujitsu</a></li> <li>VL177x series from <a href="/facts/VLSI_Technology/w3rybVFX">VLSI Technology</a>.</li> <li>Soviet KR1818WG93 (КР1818ВГ93) was a WD1793 analog</li></ul> <p>These were used in many <a href="/facts/Microcomputer/ETW22UTv">microcomputers</a> including the <a href="/facts/TRS-80/zNfQKxnQ">TRS-80</a>, <a href="/facts/Acorn_Electron/I0IDnl9N">Acorn Electron</a>, <a href="/facts/BBC_Master/IPkzMQDL">BBC Master</a>, <a href="/facts/Atari_ST/9GsYSlaM">Atari ST</a>, <a href="/facts/Acorn_Archimedes/BxInoqjT">Acorn Archimedes</a>, and the <a href="/facts/SAM_Coup%C3%A9/MwaSILTe">SAM Coupé</a>, as well as the <a href="/facts/%2BD/fIeza0u3">+D</a> and <a href="/facts/DISCiPLE/Up94HA9g">DISCiPLE</a> disk interfaces for the <a href="/facts/ZX_Spectrum/JVbaDHrU">ZX Spectrum</a>, the <a href="/facts/Commodore_1571/2DNgGToH">Commodore 157x</a>/<a href="/facts/Commodore_1581/Co9xWBnc">1581</a> for the <a href="/facts/Commodore_64/3TPcKDbb">Commodore 64</a> and the <a href="/facts/Atari_XF551/SXvrYLxI">Atari XF551</a> for the <a href="/facts/Atari_8-bit_computers/aT04N5zR">Atari 8-bit computers</a>. </p> <h2 id="further-reading">Further reading</h2> <ul><li><a href="http://www.bitsavers.org/components/westernDigital/_dataBooks/1986_Storage_Management_Products_Handbook.pdf">Western Digital Storage Management Produces Handbook</a> - describes the entire line of products.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Michalopoulos, Demetrios A (October 1976). "New Products: Single-chip floppy disk formatter/controller". Computer. 9 (10). IEEE: 64. doi:10.1109/C-M.1976.218414."The FD1771 is a single-chip floppy disk formatter/controller that interfaces with most available disk drives and virtually all types of computers." <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"Recent IC Announcements". Computer. 9 (10). IEEE: 66. October 1976. doi:10.1109/C-M.1976.218417. The FD1771 was announced on July 19, 1976, and sold for $60 each in lots of 100. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Guzis, Charles P. (2009-09-13). "Durango GCR". Sydex. Archived from the original on 2017-03-25. Retrieved 2017-03-25. <a href="http://www.vcfed.org/forum/showthread.php?17262-5-25-quot-floppy-disks-with-bad-sectors-any-solutions/page4" target="_blank">http://www.vcfed.org/forum/showthread.php?17262-5-25-quot-floppy-disks-with-bad-sectors-any-solutions/page4</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"Recent IC Announcements". Computer. 10 (12). IEEE: 140. December 1977. doi:10.1109/C-M.1977.217618. The FD1781 was announced on September 21, 1977. Supported Dual density; accommodates MFM, M2FM. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"Dual Density Floppy Controller Chip". Byte. 3 (3): 216. March 1978. <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>FD 179X-02 datasheet <a href="http://bitsavers.org/components/westernDigital/FD179X-02_Data_Sheet_May1980.pdf" target="_blank">http://bitsavers.org/components/westernDigital/FD179X-02_Data_Sheet_May1980.pdf</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>WD279X-02 datasheet <a href="http://www.lupinek.com/soubory/wd2797.pdf" target="_blank">http://www.lupinek.com/soubory/wd2797.pdf</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>WD177X-00 datasheet images <a href="http://www.zimmers.net/anonftp/pub/cbm/documents/chipdata/wd177x/index.html" target="_blank">http://www.zimmers.net/anonftp/pub/cbm/documents/chipdata/wd177x/index.html</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> </ol>