Talk:Z/OS

31-bit

A 31-bit mode? Don't you mean a 32-bit mode?

• 31-bit mode is correct. The original OS/360 operating system had 24 bit addressing. After the 31 bit mode was introduced, the 24 bit muytguiohgiulode still had to be supported. The high order bit was used to differentiate between the two addressing modes, so they only had 31 bits for the address rather than the full 32. In case you're wondering, the current OS still supports 24 bit addressing mode, and applications are still used that must be run in 24 bit mode. Dave6 19:24, 10 August 2005 (UTC)

Additionally, the high-order bit in a 4 byte address (which is known as a "full word") was utilized to denote the last address in a list of parameter addresses passed from a calling program to a called program. Ergo it was not available for use as part of the address itself. For example: a calling program passes A, B and C to a called program. The corresponding address for each variable is stored in a full word aligned to a full word boundary (i.e. addresses ending in X'0', X'4', X'8' and X'C'). The last address in this list of addresses will contain a value of X'1' in the high order bit to denote the fact that it is the last address in the list of addresses. All of this is part and parcel of what came to be known as "standard linkage conventions". —The preceding unsigned comment was added by 20.137.18.50 (talk • contribs) 18:23, 13 March 2006 (UTC).

Shorin887 just today changed a "31" into a "32" where I don't believe it should be "32". Granted REGISTERS were 32-bit but virtual and real addressing wasn't. Perhaps we should rephrase in places to reflect that divergence. But it's still "31-bit mode" to most people. Martin Packer 16:52, 6 July 2007 (UTC)

I've gone back to "31-bit", linked to the 31-bit page, referred to it as "31-bit addressing", and cleaned that sentence up a bit in other ways. Guy Harris 17:03, 6 July 2007 (UTC)

Thanks Guy! Martin Packer 17:45, 6 July 2007 (UTC)

"Robust memory protection"?

The article now speaks of z/OS having "a robust memory protection capability generally unheard of in the world of microcomputing". Presumably either "a robust memory protection capability" means something more than "putting each task in its own address space, with shared regions write-protected", or "the world of microcomputing" doesn't include Windows NT or Unix-like systems such as Mac OS X, Linux, BSD, Solaris, AIX, HP-UX, etc., as all those OSes have that level of memory protection, or "generally unheard of" means "generally unheard of in what's left of the world of microcomputing once you exclude modern OSes". Guy Harris 04:32, 14 March 2006 (UTC)

There really exists "a robust memory protection capability generally unheard of in the world of microcomputing" . This refers to the hardware protection key, a unique feature of the early /360 architecture and also of z/OS.

Hardware protection keys eliminate the risk of buffer overflows into kernel space. They isolate z/OS Subsystems from each other, and greatly improve transaction isolation e.g. in the CICS transaction server.

There exists nothing comparable in other platforms. W. G. Spruth 84.57.183.209 22:11, 1 November 2006 (UTC)

Presumably the buffer overflows to which you're referring are overflows in supervisor-mode code; user-mode code should have no write access to kernel space. That also presumably means that not all supervisor-mode code runs with protection key 0. However, that'd protect only against overflows into regions with different protection keys.

Do MVS and its successors use protection keys within a task to protect parts of the task from other parts? (Protecting one task from another should only be necessary with memory shared between tasks when different tasks have different address spaces.) Guy Harris 22:24, 1 November 2006 (UTC)

As someone who presents regularly at customer conferences for IBM on the subject of memory I can tell you z/OS's memory management is VERY sopthisticated - and getting MORE so (even in 2007). Martin Packer

The question wasn't about memory management in general; it was about memory protection. Guy Harris 21:23, 17 February 2007 (UTC)

IIRC MVS used the same protection key value for all user applications, relying on the multiple address spaces (DAT box plus Paging Supervisor) to isolate them; it used different protection keys for different parts of the OS, the least privileged keys for the parts that user apps called directly (SVCs = supervisor calls; many 3rd-party packages included their own custom SVCs). This scheme was known as "rings of confidence". Philcha 00:23, 21 October 2007 (UTC)

Style Issue

Good article, but the sentence "z/OS is IBM's flagship operating system, suited for continuous, high volume operation with high security and stability" doesn't sound objective - sounds as if sourced from sales literature. Clivemacd 10:40, 29 July 2007 (UTC)

Restructure of articles about IBM mainframe operating systems

After a big edit of MVS I concluded that the whole set of articles about IBM mainframe operating systems from System/360 onwards needed to be re-structured to minimise overlap and to make clearer the evolutionary relationships between these operating systems (notably in memory management, which is historically a major distinguishing feature). There is already some support for this proposal. Please add comments at Talk: MVS. Philcha 23:56, 20 October 2007 (UTC)

Rewrite of Job Control Language in progress

As part of the proposed restructure of articles on IBM mainframe operating systems (above), I've rewritten Job Control Language to: cover IBM's DOS/360 and its descendants as well as OS/360 and its descendants; focus more on the facilities and flavour of the 2 JCLs rather than on details of some statement types and some of their options. Please comment in Talk: Job Control Language. I'd be particulary grateful for more info on DOS/360 and its descendants, especially after 1980 - I only used DOS JCL a handful of times, and only in the late 1970s.

The rewrite does not currently take account of Truthanado's point in Talk: Job Control Language about use of "JCL" by computer suppliers other than IBM, which may entail further restructuring of articles about JCLs. Philcha 00:26, 21 October 2007 (UTC)

Suggestion for a disambiguation page

The word ZOS which redirects to this page is a metaphysical concept introduced by Austin Osman Spare. I don't know if in computer literature the word z/OS is usually replaced by ZOS or not. But I suggest to create a disambiguation page for ZOS entry. --Sepand (talk) 06:08, 30 May 2008 (UTC)

"zOS" is used instead of proper "z/OS" quite frequently (not "ZOS"; the first letter is always capitalized by Wikipedia). I would suggest creating Zos (metaphysics) stub. --Kubanczyk (talk) 08:03, 30 May 2008 (UTC)

That concept can not expand as an independent entry. Only one sentence would suffice: ZOS, an idea of Perfect Man introduced by English occultist, Austin Osman Spare. Hence I think we can place it in a disambiguation page. --Sepand (talk) 08:34, 30 May 2008 (UTC)