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From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: Super-Workbench; AmigaDOS drawer opening & directory listings
Message-ID: <2234@cbmvax.UUCP>
Date: Wed, 19-Aug-87 12:44:39 EDT
Article-I.D.: cbmvax.2234
Posted: Wed Aug 19 12:44:39 1987
Date-Received: Sat, 22-Aug-87 02:16:41 EDT
References: <3887@garfield.UUCP>
Organization: Commodore Technology, West Chester, PA
Lines: 38

in article <3887@garfield.UUCP>, john13@garfield.UUCP (John Russell) says:
> Keywords: ideas workbench
> Summary: look! feel!
> 
> If you want to see why IBM's and such have relatively fast directories, don't
> go to books of comp theory -- use the intuitive, visual approach. Rip (yeah!)
> the cover from an IBM drive and do a directory. The head just drops straight
> down onto the directory track, the disk spins, the directory prints, and
> that's it. I've done enough Disksalv's to know that, regardless of all the
> talk about hashed directory structure, all the good stuff is bunched together
> pretty well in one spot. 

Close, but no cigar, so to speak.  All of the Directories and File Headers
on a floppy do usually show up on a floppy grouped somewhere above the root
directory block at 880.  The big difference between listing an IBM directory
and listing an AmigaDOS directory is the place the filenames are listed.  You
do notice when running DiskSalv that the file names don't show up when a 
directory is encountered, but when actually when a File Header is found.  That's
because the file header contains the directory name.  The IBM keeps its file
names in its directory structure.  The result of this is twofold.  First of
all, if you're doing a directory, the IBM does one seek for a directory header
and come up with a big pile of names.  It then goes to the exact next block
and gets more names, etc.  The Amiga fetches one directory block, but then it
must do one read, implying one possible seek, for each entry in that directory.
As you mentioned, that can involve alot of head movement.  If the Amiga file
handler were optimized for track buffered floppies (what we're dealing with 
here) instead of being completely generic, this could be much faster, but it
still implies more work than an IBM directory would.  The second result of the
Amiga disk structure is that all of the directories on a disk can be completely
blown away and it's still possible for a program like DiskSalv to get them all
back, complete with file names.  You can't do this on an IBM disk.

> John
-- 
Dave Haynie     Commodore-Amiga    Usenet: {ihnp4|caip|rutgers}!cbmvax!daveh
"The A2000 Guy"                    PLINK : D-DAVE H             BIX   : hazy
     "I'd rather die while I'm living, than live while I'm dead"
						-Jimmy Buffett