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From: michael@stb.UUCP (Michael)
Newsgroups: comp.sys.amiga
Subject: Re: Initial Opinion of Amiga
Message-ID: <826@stb.UUCP>
Date: Mon, 29-Dec-86 16:34:34 EST
Article-I.D.: stb.826
Posted: Mon Dec 29 16:34:34 1986
Date-Received: Fri, 9-Jan-87 00:49:52 EST
References: <939@blia.BLI.COM> <3917@mit-eddie.MIT.EDU> <1317@hoptoad.uucp> <1910@jade.BERKELEY.EDU>
Organization: STB BBS, Los Angeles, CA
Lines: 86

In article <1910@jade.BERKELEY.EDU>, mwm@eris.BERKELEY.EDU (Mike (Don't have strength to leave) Meyer) writes:

[discussion of '/' vs. '../']

My mistake; under 1.1 I had trouble using a '/' in the middle of a path
specification to mean parent; under 1.2 there is no trouble.

> might also note that, unlike the "." and ".." kludges in Unix (you
> want to count the number of programs that KNEW that the first two
> entries in a directory were "." and ".."?

I know of none that knew the first two were that way, but a lot that knew
that they were in there somewhere. I prefer it, but that may just be my
background; it certainly is a nicer way of refering to the current directory

> Of course, it might be worth pointing out that Unix has the same
> "a-symmetry." At the beginning of the file name, it means "use the
> root directory." Everywhere else it means "we've just finished a
> directory name."

Nonsense. In unix, all files have a complete specification relative to '/';
if you begin with '/', it uses that complete spec; otherwise, it prepends
your current directory (which does begin with a '/') to make a complete
path.

[discussion of type-ahead, and console.device's clean-output type-ahead]

> Huh? I type ahead all the time. No problem, you just have to type a
> complete line. I also run "stty tostop" on Unix, which is even worse;
> you have to wait for commands to complete before finding out that
> there's output. But it's worth it; I LIKE not having garbage show up
> in the middle of a line I'm typing.

Matter of opinion; I don't like having programs block just because I'm
typing a the same time.

[discussion of directories, recovering from hits]

> Obviously. It's a function of the redundancy in the directory
> structure. Go look at the Xerox file systems for a good example of how
> to do this kind of thing right; of course, they use mucho caching

No, its redundancy in the FILE-system, not the directory-structure.

> >Second, most micro's have DOS's with this feature. Trsdos (EVERY version)
> >comes close (they miss only because they also keep a hash table which
> 
> Uh, EVERY version of TRaShDOS is STILL just one OS. CP/M (EVERY
> version :-), MS/DOS, os/9, os/1, Unix (EVERY version :-), Apple DOS,
> and MARC don't have robust file systems. Those with directory
> 
> I never worked with a TRSDOS system that had directories; how do they
> arrange for you to read the path with one read? Also, where do the put
> the information needed to recover from a hit on a directory block, and
> especially the block holding the root of the tree on that device?

Allow me to restate this. Every version of trs-dos, (thats actually
5 different O/S's or more--Model 1, model 1 version 2.7, model 3, model 2/12,
vtos, Ldos, Newdos, probably others.  The only thing they agree on is the
address to call for file opens, close, reads, and writes. They don't agree
on arguments or disk formats.)
comes close. They don't have nested directories, but there are
several unused bits that can be used for 'this is a directory'. All the
information of where a file is located is stored in the 32 or 48 bytes of
the directory (if thats not enough most of those will use another entry for
extension entries). So, with one read you get
8 file names
Whether or not it is a directory
Where on the disk the data is stored

Now, to be recoverable from a hit, just put next-block links into each sector,
just like filesystem-handler. Add a pointer back to the directory entry that
is for this file (again, like filesystem-handler.) Presto!

Oh yea--the root of a directory is stored in the boot sector. If that goes,
then you recognize the directories by their having a different DAM
(data-address-mark) on the disk. If thats not enough, the default is track
17 for trs-dos, sector 170 for NeWDOS, clyinder 20 (?) for Ldos, etc, etc.

NeWDOS and Ldos allow the user to change that. Trs-dos can be patched. Don't
know about Vtos, DblDos, Dos-plus, etc.
			Michael
-- 
Michael Gersten		ihnp4!ucla-cs!cepu!ucla-an!remsit!stb!michael
"But you can't go to war for not liking the same jokes"
"Why not? It's as good a reason as any other"