BeebMaster - Using the Byte-Back CF Drive

Using the Byte-Back
Compact Flash Drive

Secondly, the Level 3 Econet structure reserves the first sector of each cylinder for a free space bitmap. This is how the Econet keeps track of what space is free on the disc. Each sector is allocated a single bit in the bitmap, set if the sector is free and clear is the sector is occupied.

Only one sector is allocated to the bit map. It therefore follows that the maximum number of sectors per track is 8 bits per byte x 256 bytes in the bitmap = 2048 bits for sectors. If we set heads and sectors per track in WFS to values which will exceed this, then the L3 structure written to the disc will be flawed and the server partition will not operate correctly.

I have experimented with different values, and the optimum setting for a 512MB partition appears to be 1057 cylinders with 1984 sectors per cylinder. By the way, the specifics of the number of heads and sectors per track is largely irrelevant as WFSInit multiples the two together to get its sectors per cylinder, and only uses this value in its workings.

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