Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!cmcl2!rutgers!sunybcs!boulder!hao!noao!stsci!itkin From: itkin@stsci.EDU (Elliot Itkin) Newsgroups: comp.sys.amiga Subject: Re: The Next Generation Message-ID: <124@ra> Date: Thu, 3-Dec-87 16:26:07 EST Article-I.D.: ra.124 Posted: Thu Dec 3 16:26:07 1987 Date-Received: Mon, 7-Dec-87 06:29:12 EST References: <5294@ccicpg.UUCP> <2803@cbmvax.UUCP> <516@mcdsun.UUCP> <586@trwspf.TRW.COM> Organization: Space Telescope Science Institute, Baltimore, MD 21218 Lines: 14 Summary: A non-backup use for versions Versions have another use, to prevent losing a file if the system dies at a crucial moment. If you don't have versions and the system should crash just as you are overwriting your old copy, you will lose both the old copy (half trashed) and the new one (only half written). By using the sequence: 1) write new file out to open disk space, 2) update directory, 3) delete old file (with appropriate substeps), no matter when you crash you will either have the old one, the new one or both. This use of versions was used by Univac way back when. The VAX "no version limit" is new. It is also faster than the ".bak" method because you only write the file once, not read-write (old to .bak) then write out new, which is three file traversals. You can achieve the same results by ping-ponging two files but which is the most current if you forget?