§ 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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