Editing Disk density (section)

== 3½-inch media <span class="anchor" id="3.5-DD"></span><span class="anchor" id="3.5-HD"></span><span class="anchor" id="ED"></span><span class="anchor" id="TD"></span><span class="anchor" id="VHD"></span><span class="anchor" id="UHD"></span>==
''Double density'' (DD) 3½-inch disks use an iron oxide coating, just as with 5¼-inch DD/QD disks. However, drives utilize stronger 670-oersted write heads and a narrower track width of {{convert|0.115|mm|abbr=on}} for a density of 135&nbsp;tpi and 8,717&nbsp;bpi.

''High density'' (HD) 3½-inch disks switch to a cobalt disk coating, just as with 5¼-inch HD disks. Drives use 700-oersted write heads for a density of 17,434&nbsp;bpi.

''Extra-high density'' (ED) doubles the capacity over HD by using a barium ferrite coating and a special write head that allows the use of [[perpendicular recording]].<ref name="Mueller_1994_HW"/><ref name="Intel_1992_82077SL"/>

''Triple density'' (TD) triples the capacity over ED by tripling the track density and improving other parameters.<ref name="CW_1988_NEC"/><ref name="NEC_1991_uPD72070"/><ref name="NEC_PC88VA3"/> The drives used [[longitudinal recording]].<ref name="Intel_1992_82077SL"/>