27 Jul
2003
27 Jul
'03
6:34 a.m.
On Sun, 27 Jul 2003, 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?
One such way:
Have some portion of the disk set aside for a fixed number of directory
entries (the "directory").
Each directory entry has a certain number of characters for a filename (12
is good), a file type byte, a status byte, and a pointer to the portion of
the disk where the file is stored.
The file data is then stored on consecutive sectors, with the last one or
two words (depending on word size implemented) pointing to the next sector
of the file. Zero values means "end of file".
There also needs to be a map somewhere specifying which sectors are
free/used.
This is basically how most early microcomputer DOS works. I take my
example from Apple DOS 3.3.
Anything simpler would involve having files take up static areas of the
disk, perhaps defined by track boundries, with a fixed number of directory
entries (as defined by the total number of file areas) and a limited file
size (as defined by the size of each file area).
--
Sellam Ismail Vintage Computer Festival
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