Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84 SMI; site sun.uucp Path: utzoo!linus!philabs!cmcl2!seismo!harvard!talcott!panda!genrad!decvax!decwrl!sun!guy From: guy@sun.uucp (Guy Harris) Newsgroups: net.unix-wizards Subject: Re: unix file system Message-ID: <2575@sun.uucp> Date: Thu, 8-Aug-85 02:08:36 EDT Article-I.D.: sun.2575 Posted: Thu Aug 8 02:08:36 1985 Date-Received: Sun, 11-Aug-85 04:55:54 EDT References: <3287@dec-mrfort.UUCP> <5100003@rocksvax.UUCP> <3631@cornell.UUCP> Organization: Sun Microsystems, Inc. Lines: 46 > The Xerox Star file servers have a file structure which allows some > ridiculous amount of attribute data (64K?). As you might guess, attributes > in that OS are used to hold all sorts of things, including file names! The nice thing about the Pilot OS that the Star application software ran under is that the lowest level of the file system gave you the ability to refer to a file by its unique ID. It had no notion of file names whatsoever, and only supported four file attributes: Pilot recognizes only four attributes: size, type, permanence, and immutability. (From Redell, D. D.; Dalal, Y. K.; Horsley, T. R; Lauer, H. C.; Lynch, W. C.; McJones, P. R.; Murray, H. G.; Purcell, S. C., "Pilot: An Operating System for a Personal Computer", CACM 23(2): 81-92; Feb. 1980 - a good paper to read if you're interested in operating systems. Also read the retrospective "well, here's what we did right and here's what we did wrong" paper, Lauer, H. C. "Observations on the Development of an Operating System", Proceedings of the 8th Symposium on Operating Systems, in ACM Operating Systems Review 15(5): 30-36; Dec. 1981.) Anything more was up to the next level up. I'm loath to say "the application" - Pilot runs on machines with no "protected mode", limited memory protection (write-protected code pages only), and one address space for all processes, so it's not entirely clear what's "operating system" and what's "application". One advantage of storing a file name with the file "attributes" is that if the file gets lost the file system salvager can give it a better name that its unique ID in BCD when reconnecting it to a directory. (Files-11, although its basic structure is essentially the same as UNIX - i-list, called "index file", and directories which merely map names into indices - stores the file name in the "inode", and can use this when restoring the file into "lost+found", called [2,3] or something equally mnemonic. Of course, if two files with the same name are lost, so are you...) I only used a Star once; if it's directory structure is anything like what I infer the Lisa's is, it's not a problem. My model for both systems is that you have "folders" which are directories, but since files are opened by unique ID (my guess for the Lisa; that's how I would have done it, anyway) they don't have to have unique names within a directory. The names are merely for human convenience. You can open a file by pointing at it and hitting the appropriate keyboard/mouse button(s); the system knows the unique ID of the file whose icon the mouse pointer is in, so again it doesn't need the name. Guy Harris