Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!bellcore!tness7!tness1!uhnix1!sugar!peter
From: peter@sugar.uu.net (Peter da Silva)
Newsgroups: comp.sys.amiga
Subject: Re: Amiga floppies (was: Re: Blitter vs. 80386)
Message-ID: <2568@sugar.uu.net>
Date: 27 Aug 88 15:37:35 GMT
References: <8808180059.AA05505@cory.Berkeley.EDU> <2505@sugar.uu.net> <5305@killer.DALLAS.TX.US>
Organization: Sugar Land Unix - Houston, TX
Lines: 52

In article <5305@killer.DALLAS.TX.US>, elg@killer.DALLAS.TX.US
	(Eric Green) writes:
> In message <2505@sugar.uu.net>, peter@sugar.uu.net (Peter da Silva) says:
> $You're comparing apples to oranges. MS-DOS shouldn't be your standard for
> $comparison... UNIX should.

> Unix, though, still is no speed demon on searching directories,
> insofar as finding a particular program to run.

True, *but* it's way faster in getting a list of the files in a directory
and globbing wildcards. Also,

> Directories, at least
> under old AT&T versions, are sequentially organized in no particular
> order -- meaning an O(n) search time, where n is the number of files
> in all those directories.

No, this time is dominated by disk I/O, so n is the number of blocks that
have to be read off disk. At 16 bytes to a directory entry, and 512 byte
blocks, for the worst case UNIX is faster than best case AmigaDOS for up
to 32 files (it takes 2 disk accesses to verify a filename in AMigaDOS),
and just as fast for up to 64 files. I haven't figured in the effect of
hash table collisions in AmigaDOS, and on average you're going to have
half the number of accesses in UNIX.

And then...

> Of course, Unix DOES have disk caching, while MSDOS doesn't...

And AmigaDOS doesn't. Even with FACC AmigaDOS doesn't have preferential
caching of directory entries.

> and
> most Unix systems DO have faster disk drives than MSDOS machines...
> but, all in all, the performance for directory searches should be
> similiar between the two systems.

On MS-DOS, the whole file entry is stored in the directory, so there are
even fewer slots per directory entry and MS-DOS has worse directory-search
behaviour than UNIX.

I've run MS-DOS and UNIX on the same hardware. UNIX is noticably faster.
I'd like to make the same comparison on a 2500UX some time.

MOST Amiga directories have fewer than 64 files in them. About the only
directory you're going to find with worse behaviour under the UNIX file
system than the AmigaDOS one is c:. There aren't that many occasions for
large directory structures under AmigaDOS... there's no /usr/lib/termcap,
or /usr/mail, or /dev, or /usr/spool/uucp.
-- 
		Peter da Silva  `-_-'  peter@sugar.uu.net
		 Have you hugged  U  your wolf today?