IBM System/360 Model 25: Difference between revisions

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{{Short description|Low-end IBM computer model from late-1960s}}

{{Infobox information appliance

{{Infobox computing device

| name =

| titlename = IBM System/360 Model 25

| title = IBM System/360 Model 25

| aka =

| logo = File:IBM Logo 1956 1972.svg

| logo_size = 120px

| image = File:IBM 360 Model 25.JPG

| caption = IBM System/360 Model 25

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}}

The '''IBM System/360 Model 25''' is a low-end member of the [[IBM System/360]] family. It was announced on January 3, 1968, 3 years before the [[IBM System/360 Model 22]],<ref name=IBM_arch.22>{{cite web|title=IBM Archives: System/360 Model 22|url=https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP2022.html|website=IBM|date=23 January 2003|archive-url=https://web.archive.org/web/20230423095416/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP2022.html|archive-date=2023-04-23|url-status=dead}}</ref>

as a "bridge between its old and new computing systems".<ref name=IBM_arch.25>{{cite web|title=IBM Archives: System/360 Model 25|url=https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP2025.html|website=IBM|date=23 January 2003|archive-url=https://web.archive.org/web/20231210231207/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP2025.html|archive-date=2023-12-10|url-status=dead}}</ref> members of the [[IBM System/360|System/360]] family of computers.

==History==

At a time when lower priced<ref name=TaskF.rpt>{{cite newspapernews|newspaper=[[Computerworld]]|date=September 5, 1977|page=40|url=https://books.google.com/books?id=nAq5oP06EfEC&pg=PA40&lpg=PA40|title=IBM Feared Competition to 360/30 CPU - IBM Planned to Counter 360/30 Competition|author=Molly Upton|quote=If substantial inroads were made on the 30 base, a model 25 which had full compatibility, not just subset compatibility, with lower performance and lower price "would retain for IBM many installations exposed by price alone rather than by price/performance."}}</ref> alternatives<ref>'''Service, Bureaus''':such Byas [[service bureau]]s - by 1968, there were 32 such service bureaus serving the US [[National Institutes of Health]] (NIH) alone<ref>{{cite -web|title=Go East Young Man|author=Gary Myers|date=January 27, 2006|work="Information Technology Corporate Histories Collection". Computer History Museum. |url=http://www.computerhistory.org/corphist/view.php?s=stories&id=136|archive-url=https://web.archive.org/web/20060602103944/http://www.computerhistory.org/corphist/view.php?s=stories&id=136|archive-date=June 2, 2006}}</ref><ref>'''Prior - and prior generation systems''':, such as the [[Honeywell 200]], a competitor to IBM's own [[IBM 1401]].</ref>, were available, this model provided a stop-gap measure.<ref name=TaskF.rpt/>

Both the Model 25 and the Model 22, which had been marketed as entry level systems,<ref name=Pugh>{{cite book|last1=Pugh|first1=Emerson W.|last2=Johnson|first2=Lyle R.|last3=Palmer|first3=John H.|title=IBM's 360 and Early 370 Systems|url=https://archive.org/details/ibms360early370s0000pugh|url-access=registration|year=1991|publisher=MIT Press|isbn=0-262-16123-0}}</ref> were withdrawn on the same day, October 7, 1977.<ref name="IBMArchivesDates">{{cite web|url=httphttps://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_FS360.html |title=IBM Archive: System/360 datesDates and characteristics|date=23 January 2003|archive-url=https://web.archive.org/web/20230422131739/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_FS360.html|archive-date=2023-04-22|url-status=dead}}</ref>

==Models==

The Model 25<ref name=FunChar25>{{cite web|url=http://www.bitsavers.org/pdf/ibm/360/funcCharfunctional_characteristics/A24-3510-0_360-25_funcChar_Jan68.pdf|title=IBM System/360 Model 25 Functional Characteristics|publisher=IBM|date=January 1968|id=A24-3S10-0}}</ref> wascan offered with four modelsbe configured with 16K, 24K, 32K, or 48K of [[Magnetic-core memory|core memory]].<ref name=IBM_arch.25/>

==Characteristics==

The base Model 25 implements the [[IBM System/360 architecture|System/360 "universal instruction set" architecture]]. standard Theand commercial instruction setsets. is standard, and theThe scientific or universal instruction setsets is anare optional featurefeatures.<ref name="FETO"FunChar25/>{{cite bookrp|url=http://www.mirrorservice.org/sites/www.bitsavers.org/pdf/ibm/360/fe/2025/Y24-3527-0_2025_FE_Theory_Opns_Oct68.pdf|title=Field Engineering Theory of Operation, 2025 Processing Unit|id=Y24-3527-0|edition=First|date=October 1968|publisher=IBM23}}</ref>

The Model 25 logic is built on [[IBM Solid Logic Technology|IBM SLT]] modules mounted on pluggable cards, which are plugged into printed circuit boards. The boards are mounted on hinged metal gates, and are interconnected by [[ribbon cable|flat cables]].

The Model 25 wasis the first IBM system to store its [[microcode]] in a rewritable memory, called the control storage. The control storage uses an additional 16&nbsp;K (16,384) bytes of core memory.<ref name="FETO">{{cite book|url=http://www.bitsavers.org/pdf/ibm/360/fe/2025/Y24-3527-0_2025_FE_Theory_Opns_Oct68.pdf|title=Field Engineering Theory of Operation, 2025 Processing Unit|edition=First|date=October 1968|publisher=IBM|id=Y24-3527-0}}</ref>{{rp|1-3}} There is also a small part of the core storage that is used to store the contents of registers accessible by software, as well as data used by the microcode.<ref name="FETO"/>{{rp|1-4}}

The Model 25 also has a 64-byte high-speed (180&nbsp;ns) SLT Local Storage, used by the microcode.<ref name="FETO"/>{{rp|1-5}}

===Standard Features===

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*Scientific or universal instruction set

*Byte multiplexer channel or selector channel (one of either)

*StoreStorage protection

*Direct control (with external interrupt) or external interrupt (alone)

*Timer (line-frequency type)

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*1401/1440/1460 DOS compatibility

*[[IBM 1440|1440]] compatibility

*[[IBM System/360 Model 20|System/360 Model 20]] mode<ref name="FETO"/>{{rp|6-1}}<ref>{{cite book|title=IBM System/360 Model 25 Model 20 Mode Feature|publisher=IBM|id=GA24-3524}}</ref>

*CPU-integrated attachments for:

::One [[IBM 1403|1403]] Prnter Model 2 or 7. After the original announcement the IBM 1403 model N1 was added.

::As many as four [[IBM 2311|2311]] Disk Storage Drives Model l1 (with file scan feature)

::One [[IBM 2540|2540]] Card Read Punch Model 1 (with column binary feature and punch feed read control)

::One [[IBM 2560|2560]] Multi-function Card Machine Model AlA1 (for Model 20 mode; also for System/360 mode [read/punch only] if the 2540 emulation feature wasis added)<ref>{{cite book |last1=IBM Corporation |title=IBM System/360 System Summary |date=January 1974 |page=6-3 |url=http://www.bitsavers.org/pdf/ibm/360/systemSummary/GA22-6810-12_360sysSumJan74.pdf |accessdate=Nov 20, 2019}}</ref>

::CPU-integrated communications attachment

::One [[IBM 2314|2314]] High Speed Channel - this feature wasis aan [[Request price quotation|RPQ]], and was not part of the original announcement<ref>{{cite book|url=http://www.bitsavers.org/pdf/ibm/360/fe/2025/GA24-3547-0_360-25_High_Speed_Channel-2314_Attachment_Feature_RPQ_E69109_Jun70.pdf|title=IBM System/360 Model 25 High-Speed Channel-2314 Attachment Feature RPO E69109|edition=first|date=June 1970|publisher=IBM|id=GA24-3547-0}}</ref>

===Integrated Attachments===

The Model 25 hadhas a standard attachment for connection of a 1052 Model 7 console printer-keyboard, which wasis used as the operator console.<ref name=FunChar25/>{{rp|26}}

Optionally, the Model 25 couldcan have a standard System/360 [[I/O channel]], that couldcan be either a byte-multiplexor or a selector channel. For the most commonly used peripherals, such as a 2540<ref name=FunChar25/>{{rp|111}} or 2560 card reader-punch, a 1403 printer,<ref name=FunChar25/>{{rp|39}} or 2311<ref name=FunChar25/>{{rp|63}} or 2314 disk drives, optional internal attachments wereare provided. These attachments connectedconnect directly to their respective peripherals, and would appear to the operating system as if the peripherals were channel-attached.

Most unusual about the 360/25 was a feature somewhat analogous to the [[IBM System/360 Model 44]]'s integrated single disk storage drive, namely an [[History of IBM CKD Controllers#System 360 Model 25 integrated attachment|integrated attachment]].<ref name=FunChar25/>{{rp|63}}

===Compatibility Features===

The Model 25 providedprovides an optional compatibility feature that helpedhelps users of [[IBM 1400 series]] computers migrate to System/360. With the additional Compatibility Feature hardware and Compatibility Support software under DOS/360, the [[IBM 1401]]/[[IBM 1440|1440]]/1460 object programs couldcan be run in the emulation mode, with little or no reprogramming.

==System configuration==

The standard set of peripherals<ref name=FunChar25/> wasis available, although by this time customers had found their way to [[Plug compatible|IBM-compatible]] alternatives.<ref>{{cite newspapernews|newspaper=Computerworld|date=August 18, 1980|page=7|url=https://books.google.com/books?id=vpGNJfMmFswC&pg=PA7&lpg=PA7|title=STC Holds Lion's Share}}</ref><ref>{{cite newspapernews|newspaper=Computerworld|date=July 2, 1979|page=5|url=https://books.google.com/books?id=pctoxeWmstkC&pg=PA5&lpg=PA5|title=The Maverick Mainframer - Philosophical Underpinnings Distinguish CDC From Its Mainframe Competitors|author=Marcia Blumenthal}}</ref>

A typical System/360 Model 25 configuration consistedconsists of:

*IBM 2025 CPU

*IBM 1052 console printer-keyboard

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*IBM 1403 printer

*One or more IBM 2311 or IBM 2314 disk drives

*One or more magnetic tape drives, either IBM 24012415 or IBM 24152401 tapemodel drives1, attached to the selector channel (the 2401 required a 2803 control unit)

==Software==

The typical operating system for the Model 25 was [[DOS/360 and successors|DOS/360]], which was loaded from disk.

Less common was [[DOS/360 and successors#TOS/360|TOS/360]], which was loaded from tape, and, rarely, [[BOS/360]], which was loaded from punched cards. Programming was mostly in the [[COBOL]], [[IBM RPG|RPG]] and [[Assembly language|Assembler]] languages for the commercial applications that were the predominant uses of this computer, but [[Fortran|Fortran IV]] could also be used for the scientific and engineering applications, and [[PL/I]] was available.

==See also==

* [[IBM mainframe]]

* [[IBM System/360]]

==Notes==