7.4.2 - Disk Sizes

Standard disk sizes under FLEX were 35, 40 or 80 tracks, with 10, 20 or 40 sectors per track. This table shows you how much room these standard sizes provided:

Tracks Sectors/track Sectors/disk Bytes Overall Drive Configuration
35 10 340 85,680 35 track, Single Sided, Single Density
35 20 680 171,360 35 track, Single Sided, Double Density
35 20 680 171,360 35 track, Double Sided, Single Density
35 40 1360 342,720 35 track, Double Sided, Double Density
40 10 390 98,280 40 track, Single Sided, Single Density
40 20 780 196,560 40 track, Single Sided, Double Density
40 20 780 196,560 40 track, Double Sided, Single Density
40 40 1560 393,120 40 track, Double Sided, Double Density
80 10 790 199,080 80 track, Single Sided, Single Density
80 20 1580 398,160 80 track, Single Sided, Double Density
80 20 1580 398,160 80 track, Double Sided, Single Density
80 40 3160 796,320 80 track, Double Sided, Double Density

If you're paying attention, you may have noticed that the calculations shown here are "short" by one track.

The track that is not counted in these calculations is used in all formats to hold the directory of files for the disk. In unusual cases, there may be enough files on a disk to require more directory space than the first reserved track; in that case, FLEX will automatically add sectors to the directory from the currently unused data sectors. Alternatively, there is a utility provided called "extend" which will reserve a block of sectors if you know ahead of time that you will be placing an unusually large number of files on a disk. Extending a directory this way makes the directory searches run faster on a floppy system; within this emulated system, the file I/O is not noticeably affected by fragmentation.

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