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Storage Module Device
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<h2 id="cdc-976x-disk-geometry">CDC 976x disk geometry</h2> <p>The CDC 9762 80 MB variant has 5 × 14" platters. The top and bottom platters are guard platters and not used for storage. The top and bottom guard platters are exactly the same size as the data platters, and are usually made from a data platter which had too many errors to be usable as a data platter. The remaining 3 platters give 5 data surfaces and one servo surface for head positioning, being the upper surface of the center platter. </p><p>The CDC 9766 300 MB variant has 12 × 14" platters. Again the top and bottom platters are guard platters and not used for storage. The remaining 10 platters give 19 data surfaces and one servo surface for head positioning, again being the upper surface of the center platter. </p><p>Common to both the 80 MB and 300 MB disks, they have 823 cylinders and the servo surface is on one of the central platters. The sector size and sectors per track depend on how the disk is initialized. For example on the <a href="/facts/GEC_4000_series/bwDmUUH6">GEC 4000 series</a> minicomputers a configuration of 34 sectors of 512 data <a href="/facts/Byte/BNHUp9Qq">bytes</a> each per track is used. </p><p>SMD <a href="/facts/Disk_pack/UQsR6R3G">disk packs</a> (as the Storage Module itself was most commonly called) required <a href="/facts/Disk_pack/UQsR6R3G">head alignment</a> to assure interchangeability of media between drives. </p> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Control Data Corporation Newsletter, Summer 1977 Edition, p. 6 <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Control Data Corporation Newsletter, Summer 1977 Edition, p. 6 <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Control Data Corporation Newsletter, Summer 1977 Edition, p. 6 <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Control Data Corporation Newsletter, Summer 1977 Edition, p. 6 <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Glass, Brett (February 1989). "Hard Disk Interfaces". BYTE. pp. 293–297. Retrieved 2024-10-08. <a href="https://archive.org/details/eu_BYTE-1989-02_OCR/page/n350/mode/1up?view=theater" target="_blank">https://archive.org/details/eu_BYTE-1989-02_OCR/page/n350/mode/1up?view=theater</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Magnetic Peripherals Corp. Magazine, August 10, 1981 <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>1984 Disk/Trend Report <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> </ol>