Having the information about the contents of a volume on the volume itself allows the volume to be used on more than one system. If that information was stored in the catalog, that would not be practical.
DASD devices were not nearly as reliable as they are today, even without RAID. When a volume is restored to a new volume, all of the information about the contents of the restored volume is included on the volume itself. Catalogs relieve the need to specify which volume contains a data set in the JCL. A volume can be DASD or tape. Some early DASD devices for system/360, like the 2311 and 2314 could be dismounted and a different volume mounted in its place. It was not uncommon to have many more volumes than drives. -- Tom Marchant On Thu, 23 May 2024 22:32:28 -0400, Phil Smith III <[email protected]> wrote: >I'm curious whether any of you old-timers can explain why we have both VTOCs >and catalogs. I'm guessing it comes down to (a) VTOCs >came first and catalogs were added to solve some problem (what?) and/or (b) >catalogs were added to save some I/O and/or memory, back >when a bit of those mattered. But I'd like to understand. Anyone? ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
