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{{Short description|IBM mainframe operating system designed for use with smaller machines}}
{{About|the family of operating systems for IBM System/360 computers||DOS (disambiguation)}}
{{History of IBM mainframe operating systems}}
'''Disk Operating System/360''', also '''DOS/360''', or simply '''DOS''', is the discontinued first member of a sequence of [[operating system]]s for [[IBM System/360]], [[System/370]] and later [[IBM mainframe|mainframes]]. 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
==DOS versions==
===BOS/360===
{{main|BOS/360}}
The '''Basic Operating System''' (BOS) was an early version of DOS and TOS which could provide usable functionality on a system with as little as 8 KB of main storage and one 2311 disk drive.<ref>{{cite book |last1=IBM Corporation |title=IBM System/36D Basic Operating System Programmer's Guide |date=Sep 1967 |url=http://bitsavers.org/pdf/ibm/360/bos_bps/C24-3372-6_BOSpgmr_Sep67.pdf |access-date=Jan 24, 2022}}</ref>
===TOS/360===
'''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|mailing-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=39–40|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]].
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===DOS/VS===
'''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 |
DOS/VS increased the number of partitions (separate simultaneous programs) from three (named Background, Foreground 1 and Foreground 2) to five (BG and F1 through F4) and allowed a system wide total of fifteen subtasks.<ref name=GC33-5370>{{cite book|last=IBM Corporation|title=Introduction to DOS/VS Release 29|year=1973}}GC33-5370-2</ref>{{rp|pp.24–28}}
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|id = SA22-7070-0
}}</ref> DOS/VSE provided support for ECPS:VSE, but could also run on a System/370 without that feature. VSE was the last free version of DOS.
===VSE/AF===
'''VSE/Advanced Functions'''<ref>{{cite book
| title = VSE/Advanced Functions Program Summary
| id = GC33-6157-0
| quote = Together with the DOS/VSE SCP (system control programming), VSE/Advanced Functions provides operating system support for IBM processing units listed in the "Machine Requirements" section.
| url = http://bitsavers.org/pdf/ibm/370/DOS_VSE/GC33-6157-0_IBM_VSE_Advanced_Functions_Program_Summary_V1R3M5_5746-XE8_198306.pdf
| access-date = January 24, 2022
| publisher = IBM
}}
</ref> (VSE/AF), prepared for 1983 delivery, added new device support and functionality to DOS/VSE. Many installations ran VSE/AF using products such as VSE System Installation Productivity Option/Extended (VSE System IPO/E), which combined DOS/VSE, VSE/AF and various other products.
===SSX/VSE===
[[Image:IBM Böblingen Entwicklung und Forschung briefing center during installation1984.jpg|thumb|right|An IBM staffer installing a third-party application running on SSX/VSE, at the IBM Böblingen facility where SSX work was done]]
'''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/books?id=qpTn_XtzdAMC&pg=PA46|journal=Computerworld|volume=18|issue=40|pages=46}}</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/books?id=94T9BTjdzT0C&pg=PA7|journal=Computerworld|volume=15|issue=47|pages=7}}</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/books?id=Wz-oh7ZQo8MC&pg=PA2|journal=Computerworld|volume=16|issue=11|pages=1–2}}</ref>
===VSE/SP===
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
===VSE/ESA===
VSE/ESA was a 31-bit DOS/VSE version, which was released in 1990 with support for up to 384 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|
===z/VSE===
{{main|z/VSE}}
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 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
==History ==
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* DOS/360 for machines with at least 16 KB memory and a [[disk drive]],
* TOS/360 for machines with at least 16 KB memory and a [[tape drive]].<ref group=NB>DOS/360 and TOS/360 had the same code base; the difference was whether it used disk libraries or tape libraries.</ref>
When OS/360 was finally released, a year late, it required at least 64 KB of memory. DOS was designed to use little memory, and could run on 16 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 KB of memory was later released. Despite its limitations, DOS/360 became the most widely used operating system for processors with less than 256 KB of memory{{
DOS/360 was the operating system which filled the time gap between the announcement of the System/360 and the availability of the intended operating system, OS/360. As a result of the delay, a number of customers implemented DOS systems and committed significant investments to run them. IBM expected that DOS/360 users would soon upgrade to OS/360, but as a result of those investments, they were reluctant to commit to such conversion. IBM then needed to continue to offer DOS/360 as an additional operating system. The [[Hacker's Jargon File]] incorrectly states that [[GECOS]] (also known as GCOS) was copied from DOS/360, which was not the case, however the [[Xerox Data Systems]] [[Xerox Operating System]] (XOS) was intentionally similar to DOS to simplify program porting.
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The concept of transient area is part of [[The Mythical Man-Month|Mythical Man-Month]]'s discussion on design and the use of main memory.<ref>{{cite book
|title=The Mythical Man-Month |year=1975 |page=101
|author=F. P. Brooks |publisher=Addison-Wesley Publishing Company |isbn=0-201-00650-2}}</ref> To further reduce memory usage, the supervisor employed overlays called ''transients'' that were read into one of two reserved ''transient areas'' as required.
* Physical transients were loaded into the 556 byte A-Transient area to handle hardware errors (ERPs), record error-specific data (OBR/MDR) on IJSYSRC, and issue error messages. All A-Transient module names began with {{mono|$$A}}.
* Logical transients were loaded into the 1200 byte B-Transient area to
The use of {{mono|$$A}} and {{mono|$$B}} prefixes ensured rapid loading of transients because their names were stored first in the directory.
DOS/VS added Machine Check and Channel Check Handlers, which were another set of transients all starting with {{mono|$$RAST}} and executing in the Recovery Transient area. This was done as part of the reliability, availability, and serviceability (RAS) enhancements for the [[System/370]]. Before this addition, machine checks caused termination of the program running and channel checks caused termination of the program accessing the device, at the time of the error.
===Multiprogramming===
Like
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.
===Program libraries===
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
===Utilities===
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===Telecommunications===
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
==Job control==
==Job control<ref name=ControlStatements>{{cite book|last=IBM Corporation|title=System/360 Disk Operating System User's Guide: Control Statement Techniques|year=1967|url=http://www.bitsavers.org/pdf/ibm/360/dos/GC20-1685-0_Disk_Operating_System_Users_Guide_Control_Statement_Techniques_Dec69.pdf}}</ref>==▼
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''
* The {{code|JOB}} statement indicates "the beginning of control information for a job." The format is <syntaxhighlight lang="jcl" inline>// JOB <jobname> <comments></syntaxhighlight>. {{mono|<jobname>}} must be one to eight alphanumeric characters to identify the job. {{mono|<comments>}} are ignored.
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* The {{code|MTC}} statement issues command to a magnetic tape unit. The format is <syntaxhighlight lang="jcl" inline>// MTC <opcode>,SYSxxx[,<nn>]</syntaxhighlight>. {{mono|<opcode>}} is a function such as "FSF" to forward space one file or "REW" to rewind the tape. {{mono|<nn>}} is a number that can specify the number of times the operation is to be performed, such as forward space two files.
* The {{code|VOL}} statement provides disk or tape volume label information for standard label checking. The format is <syntaxhighlight lang="jcl" inline>// VOL SYSxxx,<volume></syntaxhighlight>.
* 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 [[
▲
==Differences from OS/360==
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===Spooling===
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
===Program loading===
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{{IBM operating systems}}
{{Disk operating systems}}
{{DEFAULTSORT:DOS 360 and successors}}
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[[Category:IBM mainframe operating systems]]
[[Category:Assembly language software]]
[[Category:1965 software]]
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