Talk:CMS file system

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Minidisk (CMS)

It seems that Minidisk (CMS) redirects here. Maybe that isn't so bad, but it also doesn't seem right. VM(CP) minidisks can be formatted in any (or no) disk format, likely including those of OS/360 or MVS. Is there enough for an article on minidisks, separate from CMS? The reason I am wondering is discussion on History of IBM magnetic disk drives which leaves open the question about physical or logical devices. With devices like the 3390-A, which are logical even as seen without any OS, there should be somewhere discussed the idea of logical disk drives. Gah4 (talk) 00:10, 8 May 2021 (UTC)[reply]

@Gah4: Maybe a separate section in the CP/CMS article would be better? It was a unique feature of CP when it was introduced(?). Is there any material on where the idea came from? It certainly influenced many later systems including the PC-DOS partition tables. Peter Flass (talk) 01:29, 8 May 2021 (UTC)[reply]

There is also VM_(operating_system) and probably others. I am trying to understand all the ways that disks are virtualized, and how they should be discussed here. There is, for example, Network File System though that is at a higher level, but still... Gah4 (talk) 02:35, 8 May 2021 (UTC)[reply]

@Peter Flass: I've added a generic description of minidisks to VM (operating_system) and updated my footnote to CMS file system to mention when cuu became irrelevant. Shmuel (Seymour J.) Metz Username:Chatul (talk) 10:23, 11 May 2021 (UTC)[reply]

It seems that minidisks should be discussed in Storage virtualization, although that article seems to be a mishmash. The lede says it's about I/O device virtualization, but it then seems to go on to talk about virtial storgage. Is the minidisk the earliest example of virtual disks? It would be nice to say that somewhere. Peter Flass (talk) 15:25, 11 May 2021 (UTC)[reply]

CP-67 is the first virtualization of disks that I'm aware of, but ASP and HASP virtualized unit record equipment, and DCS may have. 17:14, 11 May 2021 (UTC)Shmuel (Seymour J.) Metz Username:Chatul (talk)

Virtualization can be used to describe many different ways of doing things different from the original design. Mentioning ASP reminds me of its use of CTCs in its virtualizing. Given that IBM had the CTC, what all did they do with it? It is pretty much perfectly designed for virtualization of channel attached devices. The earliest OS/360 tests were run emulated on 7090s, as that is what they had. I presume also with virtualized disks. But I suppose they didn't sell those, so they aren't a product. But was CP-67 a product? Does it count if it wasn't? ASP was interesting, as it rewrites the JCL to reference the CTC device, instead of just pretending like HASP. And then there is the ASP VCTC, virtualization of the CTC when on the same machine. Gah4 (talk) 21:52, 11 May 2021 (UTC)[reply]

With ASP the CTCA looked like a tape drive; with HASP you had virtual readers, printers and punches; I don't know how DCS handled it. CP-67 was a type 3 program: no charge, no support. Shmuel (Seymour J.) Metz Username:Chatul (talk) 22:08, 11 May 2021 (UTC)[reply]

The thing about JCL and access methods, is that users can write programs without needing to know so much detail about the I/O devices. One can change the JCL and write to disk instead of SYSOUT=A. As far as I know, even on the lowest levels of OS/360, output is still spooled, though input might come from a card reader. Virtualization can be done at the device level, controller level, I/O instruction level, device driver level, or (when applicable) file system level. (Probably more that I didn't think about.) The actual implementation can be very different, but we call them all virtual. Gah4 (talk) 23:40, 11 May 2021 (UTC)[reply]