#: 4811 S10/Tandy CoCo
    01-Jul-90  21:15:20
Sb: #4809-os9 Disk Zapp
Fm: Pete Lyall 76703,4230
To: Denise Tomlinson 71021,3274 (X)

Denise -

Basically the disk is broken up into the following areas:

  o - LSN0 (logical sector # 0)

  o - storage bitmap

  o - File descriptor sectors

  o - Directories and files

The LSN0 contains all the crucial info about the disk (heads, cylinders,
allocation strategy, etc.). It is the 1st sector on the media. It is followed
by the bitmap. The bitmap is a series of sectors full of bytes that represent
what part of the disk is used, and what part is free. Typically, a bit in the
bitmap = 1 sector on the disk (although clustersize may be set to be greater
than 1 sector, and then each bit represents 1 cluster). The size of the bitmap
is recorded in the LSN0 sector. The File descriptor sectors are the map for
each file or directory. They contain information on date of creation, owner,
size, attributes, etc. in the 1st 16 bytes. The other 240 bytes of the sector
are 48 5-byte records of the form:

   LSN(3) #ofSectors(2)

Indicating where the file is mapped on the disk. The 1st 3 bytes show the
starting logical sector number of the chunk, and the next two show how many
sectors are in that chunk. The FD sector for the root directory is specified by
LSN # in the LSN0 sector. From there, you can find the root directory, and all
files and directories below it. All directory entries are of the form:

  Name(29) LSN(3)

Where name is up to 29 bytes long (last character has the high bit set), and
then 3 bytes tat indicate the LSN of the FD sector for that file.

You can get more information by reading about the RBF manager in the technical
reference manual. Hope that was enough to get you started.

Pete