POKing Around On The Fixed Disk
 
                               Chris Thomas
                                   UCLA
 
The other day I was investigating how many files I could put on my fixed
disk.  The DOS manual indicated that the format of the disk depends on how
much of it is allocated for DOS. So I POKEd around and found that when
allocated entirely for DOS use, the 20740 sectors on the 10MB Fixed Disk
are allocated as follows:
 
                      # of
                     Sectors            Use
                     --------        -----------
                     1       System boot and partition map
                     1       DOS boot record
                     8       FAT
                     8       FAT - duplicate copy
                     32      Directory
                     20688   Data sectors (2586 clusters)
                     2       Unused sectors(not mapped
                               by FAT)
                     68      Cylinder 305, used by
                               diagnostic routines
 
There are eight sectors per cluster, meaning the smallest file takes 4K.
This is necessitated by the architecture of the File Allocation Table,
which allows a maximum of 4087 clusters.  The directory has space for 512
files, unless there is some other limitation in DOS.
 
One result of this exploration is that I feel much pressure to use
subdirectories to keep from running out of directory space.  Although
subdirectories are fine for some data, many things only coexist with
subdirectories and don't actually support them.