DOS/360 and successors: Difference between revisions

'''Disk Operating System/360''', also '''DOS/360''', or simply '''DOS''', is athe discontinued first member of a sequence of [[operating system]]s for [[IBM System/360]], [[System/370]] and later [[IBM mainframe|mainframes]]s. It was announced by [[IBM]] on the last day of 1964, and it was first delivered in June 1966.<ref>{{cite book |first1=E.W. |last1=Pugh, |first2=L.R. |last2=Johnson, and |first3=John H. |last3=Palmer, ''|title=IBM's 360 and early 370 systems,'' |date=1991 |publisher=[[MIT Press,]] |location=Cambridge, MA and London, {{ISBN|isbn=0-262-16123-0}}<br/>&ndash; extensive (819&nbsp;''pp.'') treatment of IBM's offerings during this period</ref> In its time, DOS/360 was the most widely used operating system in the world.<ref>Pugh, ''op. cit., p.'' 331 &ndash; most widely used OS</ref>

'''TOS/360''' (Tape Operating System/360, not a DOS as such and not so called) was an [[IBM]] [[operating system]] for the [[System/360]], used in the early days around 1965 to support the [[IBM System/360 Model 30|System/360 Model 30]] and similar platforms.

TOS, as per the "Tape" in the name, required a tape drive. It shared most of the code base<ref name=40Y.mem>{{cite newsgroup|url=https://groups.google.com/d/msg/alt.folklore.computers/RZA6FD27Tc0/-LoIXsOee7gJ|title=DOS/360: Forty years|author=Joe Morris|newsgroup=alt.folklore.computer|date=April 25, 2005|quote=Don't forget TOS, the bastard cousin of DOS. Either could be generated from the same set of distribution libraries...}}</ref> and some manuals<ref>{{cite web|url=http://www.bitsavers.org/pdf/ibm/360/dos/GC24-5030-8_Disk_and_Tape_Operating_Systems_Concepts_and_Facilities_Oct70.pdf|title=IBM System/360 Disk and Tape Operating Systems Concepts and Facilities|date=October 1970|id=GC2ij-5030-8}}</ref><ref>{{cite web|url=http://www.bitsavers.org/pdf/ibm/360/dos/GC24-3465-8_DOS_and_TOS_Utility_Programs_R26.1_Aug73.pdf|title=DOS and TOS Utility Programs|date=August 1973|id=GC24-3465-8}}</ref> with IBM's DOS/360.

TOS went through 14 releases, and was discontinued<ref>{{cite mailing list|url=https://www.mail-archive.com/ibmvm@listserv.uark.edu/msg24371.html|author=Anne and Lynn Wheeler|title=Re: IBM 1401|date=May 28, 2009|mailinglistmailing-list=ibmvm@listserv.uark.edu}}</ref>{{failed verification|date=July 2019}} when disks such as the [[IBM 2311]] and [[IBM 2314]] became more affordable at the time of System/360,<ref>{{cite magazine|magazine=Computerworld|date=September 5, 1977|volume=11|issue=36|pages=39-4039–40|title=IBM Feared Competition to 360/30 CPU|url=https://books.google.com/books?id=nAq5oP06EfEC&pg=PA39}}</ref>{{failed verification|date=July 2019}} whereas they had been an expensive luxury on the [[IBM 7090]].

'''DOS/VS''' was released in 1972. The first DOS/VS release was numbered "Release 28" to signify an incremental upgrade from DOS/360.<ref name=Boeblingen>{{cite web|last=IBM Corporation |title=IBM Geschichte im Jahr 1970 |url=http://www-05.ibm.com/de/entwicklung/1970.html |accessdateaccess-date=May 31, 2012 |language=German |df=de }}</ref> It added [[virtual memory]] in support of the new [[System/370]] series hardware. It used a fixed [[page table]] which mapped a single [[address space]] of up to 16 megabytes for all partitions combined.

'''SSX/VSE''' ("Small System Executive") was an attempt by IBM to simplify purchase and installation of VSE by providing a pre-generated system containing the OS and the most popular products.<ref>{{Cite journal|date=1 Oct 1984|title=IBM adds SSX/VSE aid; offers DS/VSE frontend|url=https://books.google.com.au/books?id=qpTn_XtzdAMC&pg=PA46|journal=Computerworld|volume=18|issue=40|pages=46|via=}}</ref> SSX was released in 1982,<ref>{{Cite journal|last=Paul|first=Louis|date=23 Nov 1981|title=IBM brings out simplified operating system|url=https://books.google.com.au/books?id=94T9BTjdzT0C&pg=PA7|journal=Computerworld|volume=15|issue=47|pages=7|via=}}</ref> and later replaced by VSE/SP. SSX was sold by IBM as a bundle of 14 component products (Advanced Functions/VSE, VSE/POWER, ACF/VTAME, VSE/VSAM, CICS/DOS/VS, DOS/VS, Sort/Merge, VSE/ICCF, VSE/OCCF, VSE/IPCS, DOS/COBOL, Back Up/Restore, Space Management, VSE/DITTO), and originally would only agree to offer the individual products separately via [[Request price quotation|RPQ]], although IBM later agreed to add those products individually to its price list under pressure from ISVs who claimed that the bundling violated antitrust laws.<ref>{{Cite journal|last=Blumenthal|first=Marcia|date=15 Mar 1982|title=IBM yields to Adapso heat, unbundles SSX programs|url=https://books.google.com.au/books?id=Wz-oh7ZQo8MC&pg=PA2|journal=Computerworld|volume=16|issue=11|pages=1–2|via=}}</ref>

In 1986 IBM released '''VSE/SP''' ("System Product") in conjunction with the announcement of the [[IBM 9370|9370]] processors. VSE/SP replaced SSX/VSE and bundled VSE with the most popular VSE program products such as VSE/AF, [[VTAM#ACF.2FVTAM|ACF/VTAM]], [[CICS]], and [[IBM PowerPOWER (software)|POWER/VS]].<ref>{{cite web|last=IBM Corporation|title=IBM VSE/SYSTEM PACKAGE (VSE/SP), VERSION 3 RELEASE 1.1 ENHANCED AND AVAILABLE|date=30 June 1987 |url=http://www-01.ibm.com/common/ssi/cgi-bin/ssialias?subtype=ca&infotype=an&appname=iSource&supplier=897&letternum=ENUS287-332&open&cm_mmc=5733-_-n-_-vrm_newsletter-_-10207_134134&cmibm_em=dm:0:12046832|accessdateaccess-date=June 1, 2011}}</ref> VSE/SP supported only 24-bit addresses, despite customer requests to provide an XA (31 bit) version.

VSE/ESA was a 31-bit DOS/VSE version, which was released in 1990 with support for up to 384&nbsp;MB of real storage. It provided up to twelve ''static partitions'' and allowed VSE/POWER and ACF/VTAM to be run in ''private address spaces''. It introduced a new feature called ''dynamic partitions'' which could allow up to 150 concurrent jobs, each in its own address space.<ref name=VSEESAAnnounce>{{cite web|last=IBM Corporation|title=IBM VSE/ENTERPRISE SYSTEMS ARCHITECTURE VERSION 1 RELEASE 1|date=5 September 1990 |url=http://www-01.ibm.com/common/ssi/cgi-bin/ssialias?infotype=an&subtype=ca&appname=Demonstration&htmlfid=897/ENUS290-513|accessdateaccess-date=May 31, 2012}}</ref> Version 1 could run in either ESA or 370 mode, with the ESA mode also supporting XA hardware with limitations. Version 2 (1995) only supported ESA mode with ESA hardware. Version 2 added support for [[multiprocessing]], through the new ''Turbo Dispatcher'', which permits different partitions to execute simultaneously on different processors. A partition can only run on one processor at a time, which mostly limits the multiprocessing to [[Computer multitasking|multitasking]]. Up to ten processors are theoretically supported ("tolerated"), but up to four are effectively utilized.<ref>{{cite web |title=VSE/ESA Version 2 Release 1 and VSE/ESA Languages -- PL/I, COBOL, LE Software Announcement | date=13 September 1994 |url=https://www.ibm.com/common/ssi/ShowDoc.wss?docURL=/common/ssi/rep_ca/9/897/ENUS294-519/index.html&lang=en-ZZ-ZZ |publisher=IBM}}</ref><ref>{{cite web |title=VSE/ESA Turbo Dispatcher Guide and Reference |url=https://ibmdocs.pocnet.net/SC33-6797-00.pdf }}</ref> Those limits remain in the last z/VSE.<ref>{{cite web |title=The z/VSE Turbo Dispatcher |url=https://www.ibm.com/docs/en/zvse/6.2?topic=SSB27H_6.2.0/fa2pl_zvse_turbo_dispatcher.htm |publisher=IBM}}</ref>

IBM released z/VSE 3.1 in 2005. This change in naming reflected the new "System z" branding for IBM's mainframe product line, but did not represent a fundamental change in architecture from VSE/ESA 2.7 which preceded it. In particular, it did not support the new 64-bit z/Architecture, running only in 31-bit mode even on 64-bit capable machines. z/VSE 4.1 released in 2007 introduced support for 64-bit real addressing, with up to 8&nbsp;GB of memory. However, while parts of the supervisor run in 64-bit mode, it only provides 31-bit virtual address spaces to problem state applications. As of 2011 one estimate placed the number of sites using z/VSE at around 40004,000.<ref>{{cite mailing list|url=https://groups.google.com/d/msg/bit.listserv.vse-l/g3fv5ROPc_4/Oc9Y7rGg7zkJ|title=IBM DOS, DOS/VS, DOS/VSE, VSE/SP, VSE/ESA, z/VSE Customers|mailing-list=VSE-L|date=November 2, 2011|accessdateaccess-date=April 25, 2017}}</ref>

When OS/360 was finally released, a year late, it required at least 64&nbsp;KB of memory. DOS was designed to use little memory, and could run on 16&nbsp;KB machines, a configuration available on the low-end [[IBM 2030|S/360 model 30]]. Unlike OS/360, DOS/360 was initially a single-job system which did not support [[Computer multitasking|multitasking]]. A version with multitasking, supporting up to three [[Memory management (operating systems)#Partitioned allocation|memory partitions]], requiring 32&nbsp;KB of memory was later released. Despite its limitations, DOS/360 became the most widely used operating system for processors with less than 256&nbsp;KB of memory{{cncitation needed|date=September 2017}} because: System/360 hardware sold very well; DOS/360 ran well on System/360 processors which medium-sized organizations could afford; and it was better than the "operating systems" these customers had before.

Like all System[[OS/360 operating software]], initial releases of DOS could run only one program at a time. Later versions of "real" DOS were able to run up to three programs concurrently, in separate memory partitions, supported by the same hardware memory protection features of the more scalable OS/360 operating system. These were identified as BG (''background''), F1 (''foreground&nbsp;1'') and F2 (''foreground&nbsp;2''). Multiprogramming was an optional feature of DOS/360, selectable at [[system generation]].<ref name=sysgen>{{cite book|last=IBM Corporation|title=IBM System/360 Disk Operating System: System Generation and Maintenance|year=1969|url=http://www.bitsavers.org/pdf/ibm/360/dos/C24-5033-7_Disk_Operating_System_System_Generation_and_Maintenance_Apr69.pdf}}</ref>{{rp|p.34}} A later SYSGEN option allowed [[Batch processing|batch]] operation run in either FG partition. Otherwise foreground programs had to be manually started by the [[computer operator]].

DOS-/VS allowed up to seven concurrent programs, although five or six was a more common number due to the smaller scale of the hardware usually hosting DOS systems. Both DOS and DOS-/VS allow the number of partitions to be set at [[Initial Program Load#IBM Initial Program Load|IPL]] (Initial Program Load), the IBM term for Boot load.

Executable programs were stored in a ''Core Image Library''. While running, DOS could not reclaim space as programs were deleted or replaced with newer versions. When the Core Image Library became full, it had to be compressed by one of thea utility programsprogram, and this could halt development work foruntil asit much as half awas daycomplete. Many shops simply froze changes for a day, compressed the CIL "off-line", and IPLed with the new Core Image Library at the beginning of a business day. A ''relocatable library'' for linkable object programs and a ''source statement library'' for assembler macros and include text were also supported. Installations could define additional ''private'' relocatable and source statement libraries on other disk volumes.

DOS/360 offered Basic Telecommunications Access Method ([[BTAM]]) and Queued Telecommunications Access Method ([[QTAM]]). BTAM was primitive and hard to use by later standards, but it allowed communication with almost any type of terminal, which was a big advantage at a time when there was little standardization of communications protocols. The simplicity of its API also allowed the relatively easy interface of external communications processors, which facilitated DOS/360 machines becoming nodes in the multi-tier networks of large organizations. Conversely, QTAM users didn'tdid not need as much knowledge about individual devices because QTAM operated at the logical level using the OPEN/CLOSE/GET/PUT macros.

All DOS job control statements began with "{{mono|//}}" in card columns one and two except ''end-of-job'' which was "{{mono|/&␢}}", ''end-of-data'', "{{mono|/*␢}}", and ''comments'' , "{{mono|*␢}}". (''In the description that follows the character "{{mono|␢}}" represents a single blank''.)

* DOS originally provided the {{code|TPLAB}} statement for tape label information and the {{code|DLAB}} and {{code|XTENT}} statements for disk label and extent information. At least as early as 1968 the {{code|TPLAB}} statement had been replaced by {{code|TLBL}} and the {{code|DLAB}} statement by {{code|DLBL}} . These statements used numerous [[Job_Control_LanguageJob Control Language#Positional_parametersPositional parameters|positional parameters]] and had fairly high information densities.

Early DOS included no [[spooling]] sub-system to improve the efficiency of [[punched card]] and [[line printer]] I/O. By the late 1960s both IBM and aftermarket vendors began filling this void. IBM's spooler was an option called [[IBM PowerPOWER (software)|Priority Output Writers, Execution processors and input Readers (POWER)]], and Software Design, Inc., an independent software company, sold a spooler called [[Grasp (softwarespooler)|GRASP]].

[[Category:SoftwareAssembly writtenlanguage primarily in assembly languagesoftware]]