Re: file names.number of characters

[dempson@actrix.gen.nz (David Empson)]

In article <2o1h9k$r74@gap.cco.caltech.edu>,
Nathan Mates <nathan@cco.caltech.edu> wrote:
> 
>    MS-DOG^HS was designed as a clone of CP/M, a rather ancient,
> unpowered, and short-lived OS. (It attracted a little bit of a
> following for a while, but when I looked at it, it compared
> unfavorably to MS-DOS (yeah, that's possible), so I never touched it
> again).

No arguments about CP/M comparing unfavourably to MessyDOS 2.0 and
later, but you'd be suprised how popular it was.  It first came out in
about 1976, and was quite popular until the mid-80s (IMHO).  We used
it at work until 1989 (when we switched to MessyDOS), and I still have
a CP/M computer there for accessing old files.

> The 3-char file extension is due to the fact that the set of capital
> letters fills 5 bits, and so three of those fill (with some space) 2
> bytes of disk/memory space in CP/M.

Unless you're talking about CP/M 1.x, which I haven't used, this is
completely wrong.  CP/M 2.0 and later store filenames as ASCII bytes -
eight bytes for the filename, and three for the extension.  The high
order bit of some of the bytes are used as flags.  The whole directory
entry is 32 bytes, I think.  One entry is required for each "extent",
which corresponds to 16 "allocation blocks" which can vary in size
between disks.  A large file may require several directory entries, but
all the allocation blocks are listed in the directory.

I don't know where the 8-and-3 filenames came from; possibly some
earlier mainframe or minicomputer operating system.

>    On the Apple II, Dos 3.3 (and its predecessors) had rather nice
> (40-char) names, with no extensions; a separate byte was used to
> identify what type of file it wasm

30 bytes, not 40.
 
>    ProDOS apparently wanted to act a little like MS-DOS or CP/M, so it
> went to much more restrictive filenames, but upped the number of
> filetypes and auxtypes things had. You win some, you lose some.

ProDOS uses the same file system as SOS, the Apple III operating
system, so it inherited SOS's limits.  I don't know why SOS was
limited to 15 characters using only upper-case letters, digits and
periods.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand