Re: What is PRODOS?

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

In article <36ilbu$6lu@nntp1.u.washington.edu>,
Ron Louie <ronlouie@u.washington.edu> wrote:
> Very nice explication, David and Airship!  BTW, I've always wondered: how 
> does ProDos-8 compare to MS-DOS, and GSOS to Windows?

Well, you can't compare GS/OS to Windows, because GS/OS has no user
interface.  You might be able to compare GS/OS + Toolbox to Windows,
but who would want to?  Windows is awful!  :-)

MS-DOS is strongly based on CP/M (with a lot more calls thrown in,
especially with MS-DOS 2.0 and later).  CP/M is a dinosaur compared to
ProDOS (I think that even DOS 3.3 has some advantages over CP/M).

MS-DOS is a full operating system, whereas ProDOS is only a disk
operating system.  It would be fairer to compare MS-DOS to SOS (the
Apple III operating system), but I've never used SOS so I can't do that.

I could compare MS-DOS to GS/OS.  GS/OS borrows many features from SOS
(apart from the obvious one of the ProDOS file system).

Just comparing the MS-DOS file system to ProDOS:

The MS-DOS FAT system (file allocation table) has some advantages, but
many disadvantages: you cannot access a file backwards without
maintaining a list of clusters used by the file, or scanning the FAT
links in ascending order each time; the entire FAT must be kept in
memory to avoid major performance hits (the same goes for ProDOS's
bitmap, but it is much smaller).

Then there is the risk of losing the entire file structure of the disk
by losing your FAT.  ProDOS has all the allocation data scattered
around the disk in index blocks, making it easier to recover lost
files if you lose your bitmap and root directory.

SOS and ProDOS have a nice programming interface.  CP/M's was messier,
MS-DOS 2.0 and later are better.

> Did the Apple systems really break new ground?

I can't think of any pioneering features of SOS or ProDOS.  Most of
the file system was borrowed from other places, with ideas taken from
UNIX in particular (tree structuring with multiple levels, though
the details are quite different).

> How important are the MS's bells and whistles?  How do they do with
> HD's, flopticals, and CD's? 

Generally by patching out parts of the operating system, either at the
driver level (emulating an MS-DOS formatted disk, possibly including
data format translation), or at the file system level (by patching out
the MS-DOS file calls in earlier versions, or through internal hooks
to do this in later versions).

They generally work seamlessly (if they work at all).  GS/OS's File
System Translator mechanism was certainly an innovation (I'm sure
others had done it, but it hasn't caught on until quite recently with
the Mac and PC operating systems).

All IMHO of course, and I'm sure there are others who would argue
about most of the above.  :-)

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand