File path formats. 2404

Rich Alderson Well from what I remember of IBMs : BOS, TOS, BPS, MFT, MVT, VS1, VS2, MVS ... clan of operating systems (But not CMS or others), for the 360 ... hardware family , the file systems are not organized as a hierarchical tree structure. There are 'ordinary' flat Sequential files, and then several named structures containing sequential pieces. There are Direct Access files with seperately addressable records, There are Parbreastioned Datasets (sort of like a book with chapters). There are Generation Datasets. THere are others that I am forgeting to mention. Each such item, 'file', is called a DATASET. Each dataset has a name its DSN , dataset name. A dataset name is of the form lovelovex.lovelove.love ..., where each subpart of the name may be 1 to 8 characters (with restrictions), and the total DSN length is restricted to be up to 44 characters. But an love.love.yyy name is just a name not a name in a three level hierarchy. i.e. questions of the type, what are all the yyy at the love.love level are meaningless. In addition to a simple DSN like A.B.C there are other forms for for example Parbreastioned Datasets, love.love(yyy) where the yyy is the name of a member of the love.love dataset. Each disk volume generally has a table of contents of the names and locations and some other information about the data sets on it. Tape reels, or media emulating tape, ie sequentia storage, do not have any tables of content. A particular dataset, (the DSN is always carried along in the file's header), may be either entered, or not, in a catalog. A catalog is like a TOC but acts across volumes, and can for example hold entries for tape datasets indicating which named reel(s) of tape contain the dataset. eg. DSN = A.B.C is on the 5 reels A1,A2, A3,A4,A5, or DSN = X.Y.Z is the 3rd file on reel UT1231. There may be multiple catalogs available an in use on a system and there are ways to indicate which catalogs to use when searching for a particular DSN, using which search order, ... Or one can specify the addressing directly using parameters on the Job Control Language (JCL). e.g (my JCL may be dated ) -jcln DD UNIT=DISK,VOL=SER=DISKAAA,DSN=A.B.C

Anyway the main point is that the file system of the IBM OS (.. MVT, MVS, ...) operating system clan for the 360 ... genus of hardware is not a hierarchical system. -- Rostyk

P.s. corrections, comments, further discussion is welcome.