IBM Type 2D
IBM Type 2D is a type of 8" floppy disk used by IBM for the 53FD drive used in the 1970s and 1980s on some mainframes and minicomputers such as the 370 and System/34. It uses MFM encoding at a track density of 48 tracks per inch and a bit density of 6,816 bits per inch, on double-sided double-density media. There are three subtypes, with different sector layouts and slightly different total storage capacity.
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985 KB
This format has an index cylinder of 26 128 byte sectors on side 0 and 26 256 byte sectors on side 1, and 74 regular data cylinders of 26 sectors of 256 bytes each per side, totalling 3,848 data sectors with a capacity of 985,088 bytes.
1,136 KB
This format has an index cylinder of 26 128 byte sectors on side 0 and 26 256 byte sectors on side 1, and 74 regular data cylinders of 15 sectors of 512 bytes each per side, totalling 2,220 data sectors with a capacity of 1,136,640 bytes.
1,212 KB
This format has an index cylinder of 26 128 byte sectors on side 0 and 26 256 byte sectors on side 1, and 74 regular data cylinders of 8 sectors of 1,024 bytes each per side, totalling 1,184 data sectors with a capacity of 1,212,416 bytes.
