27 Jul
2003
27 Jul
'03
5:34 a.m.
Bob Shannon wrote:
What is the simplest usable disk file system to
implement?
More specifically, if your going to write a disk file system from
scratch, what would be the easiest way to implement
some basic file system functionality?
How did some of the very early DOS systems allocate disk space in the
days before FAT tables, etc?
Just how simply can this be done?
The wang 2200 that I have (pre 1975) has two modes:
1) direct access. the program and read or write any absolutely address
sector, which is 256 bytes. this isn't what you asked for.
2) random access tape. the first N sectors of the disk contain a
catalog of files on the disk. an entry consists of 8 bytes of filename,
two bytes of starting sector, two bytes of final sector (or is it size?)
and an attribute byte (program/data). it is quite primitive. if you
want to create a data file, you must first reserve all the space you
will ever need for it. unused parts of the file still take up space.
if the file does grow bigger than you had already preallocated, you must
basically shuffle files around on disk to make room. when you delete a
file, it just makes a hole in your map. all sectors are allocated linearly.
it is very simple, but not too convenient.