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→Operating systems: We already distinguish between the 155 and 155-II; the 155 only supported virtual-memory OSes if you upgraded it to a 155-II. Remove some extra stuff about MVS.
 
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{{Infobox information appliance
| name = IBM System/370 Model 155
| title =
| aka =
| logo = File:IBM logo.svg
| aka =
| logoimage = IBM System370 Model 155 in Teamco a.s. =& File:IBMCo logo(1).svgjpg
| caption = IBM System/370 Model 155▼
| image =
| developer = ▼
▲| caption = IBM System/370 Model 155
▲| developer =
| manufacturer = International Business Machines Corporation ([[IBM]])
| family = [[System/370]]
| generation =
| releasedate = {{Start date|1970|06|30}}
| lifespan =
| price =
| discontinued = December 23, 1977
| unitssold =
| unitsshipped =
| media =
| os =
| os power =
| power soc =
| soc cpu =
| cpu memory =
| memory storage =
| storage memory card =
| memory card display =
| display graphics =
| graphics sound =
| sound input =
| input controllers =
| controllers camera =
| camera touchpad =
| touchpad =
| connectivity =
| platform =
| service =
| dimensions =
| weight =
| topgame =
| compatibility =
| predecessor =
| successor =
| related =
| website = {{Official website|https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3155.html}} ''IBM Archives''
}}
 
[[File:IBM_magnetic_disk_drives_3330+3333.png|thumb|The IBM 3330 <br>Direct Access Storage Facility, <br>code-named Merlin, was introduced in June 1970 for use with the IBM System/370. Its removable disk packs could hold 100 &nbsp;MB]]▼
[[File:IBM_370-145_(I198005).jpg|thumb|3 months after the announcement of <br>the 370/155 (and 165)<br> came the Model 145.<ref>{{cite web|url=https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3145.html|title=System/370 Model 145|website=IBM Archives|publisher=IBM}}</ref><br>Unlike the 155 (or 165), <br>the 145's lack of virtual memory could be rectified with a simple [[microcode]] update from a floppy disk, vs the others needing a hardware upgrade.]]
▲[[File:IBM_magnetic_disk_drives_3330+3333.png|thumb|The IBM 3330 <br>Direct Access Storage Facility, <br>code-named Merlin, was introduced in June 1970 for use with the IBM System/370. Its removable disk packs could hold 100 MB]]
 
The '''IBM System/370 Model 155''' (and the [[IBM System/370 Model 165|Model 165]]),<ref name=IBMarc.165>{{cite web|url=https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3165.html|title=System/370 Model 165|website=IBM Archives|date=23 January 2003|publisher=IBM|archive-url=https://web.archive.org/web/20230729090329/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3165.html|archive-date=2023-07-29|url-status=dead}}</ref>
were jointly announced Jun 30, 1970<ref name=IBMarc.155>{{cite web|url=https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3155.html|title=System/370 Model 155|website=IBM Archives|date=23 January 2003|publisher=IBM|archive-url=https://web.archive.org/web/20230516082850/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3155.html|archive-date=2023-05-16|url-status=dead}}</ref> as "designed for ... the Seventies." That same day [[IBM]] announced the 370/195.<ref>coming{{cite about 14 months after the announcement of the 360web|url=https:/195/www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3195.html|title=System/370 BothModel 195|website=IBM machinesArchives|date=23 wereJanuary withdrawn Feb2003|publisher=IBM|archive-url=https://web. 9, 1977archive. see org/web/20230729090333/https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP2195mainframe_PP3195.html|archive-date=2023-07-29|url-status=dead}}</ref> They were the first three models of the [[IBM System/370]] line of computers.
and https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3195.html</ref> They were the first three models of the [[IBM System/370]] line of computers.
 
Three months later a fourth IBM System/370, the [[IBM System/370 Model 145|Model 145]], was announced. Since none of them came with [[virtual memory]], "which was to be a hallmark of the 370 line",<ref name="what-course-for-the-3081">{{cite newspapernews|newspaper=Computerworld|date=November 24, 1980|page=34|url=https://books.google.com/books?id=cKmJJd7R8PIC&pg=PA34#v=onepage&q&f=false|title=What Course for the 3081?}}</ref> some said about these early members of the [[IBM System/370]] family, especially about the 165155 &and 155165, that they were not "the real 370 line."<ref groupname="NB">The 195 was noted as "at what-course-for-the time of its introduction, ... IBM's most powerful computing system-3081" and the 145's [[microcode]] could be upgraded from a floppy disk. By contrast, the 155 & 165 needed a hardware addition priced at $200,000 and $400,000 respectively</ref>
 
Three months later a fourth IBM System/370, the [[IBM System/370 Model 145|Model 145]], was announced.
==Limitations==
Some said about these early members of the [[IBM System/370]] family, looking back, that they were not "the real 370 line" because
"neither offered virtual storage capability, which was to be a hallmark of the 370 line."<ref name="what-course-for-the-3081">{{cite newspaper|newspaper=Computerworld|date=November 24, 1980|page=34|url=https://books.google.com/books?id=cKmJJd7R8PIC&pg=PA34#v=onepage&q&f=false|title=What Course for the 3081?}}</ref>
 
==Virtual memory==
The 370/155 was described as able to "run under [[DOS/360 and successors|DOS]]." Both the 155 and the larger 370/165 could "run under [[OS/360 and successors|OS/360]]." Neither machine, as announced, could run a virtual memory operating system.
The initially announced System/370 Models 155 and 165 systems did not support virtual memory.
 
wait untilIn 1972 an upgrade option was announced "to provide the hardware necessary to operate in a virtual memory mode."<ref>{{cite news|newspaper=Computerworld|date=August 15, at1973|page=17|title=First IBM DAT Box Installed|url=https://books.google.com/books?id=T3qky0Z-gc0C&pg=PA17}}</ref> Unlike the [[IBM System/370 Model 145]], which timeas early as June 1971 included the hardware necessary to support virtual memory, and for which a [[microcode]] update from a floppy disk, adding support for virtual memory, was announced in 1972, the Model 155 and Model 165 needed expensive hardware additions - $200,000 for the 155 and $400,000 for the 165 - to add virtual memory capability. theirAn upgraded 155 was known as an IBM System/370 Model 155-II.<ref>{{cite journal | author = A. Padegs | title = System/360 and Beyond | journal = IBM Journal of Research & Development | volume = 25 | issue = 5 | pages = 377–390 |date=September 1981 | publisher = IBM | doi = 10.1147/rd.255.0377}} &ndash; tables include model characteristics (Table 1) and announcement/shipment dates (Table 2). The S/370-155-II and -165-II are listed under the former but not the latter, because the upgraded systems were not formally announced as separate models. The "System/370 Advanced Function" announcement, including the -158 and -168, was the main public event.</ref>▼
==Growth path==
The initially announced systems were in many ways merely improved [[IBM System/360|IBM 360]] systems. Both were announced as
running 360 [[Operating System]]s.<ref group="NB">DOS on the 155, MFT or MVT on either machine</ref> No mention was made of [[virtual memory]]
or new operating systems.
 
==Physical memory==
The IBM System/370's basic [[Computer architecture|architecture]] was described as having been "extended, but not redesigned" from that of IBM System/360.<ref name=IBMarc.165/>
Although the joint 155/165 announcement<ref name=IBMarc.165/> did not have the word virtual, there were multiple references to (physical) memory, storage (both main memory and disk storage), and [[cache memory]] under the name "buffer".▼
 
The 155 had seven main memory choices, ranging from 256K256&nbsp;KB to 2 &nbsp;MB; the 165: five possibilities, from 512K512&nbsp;KB to 3 &nbsp;MB. Both models were described as having "a very high-performance buffer storage backed by a large" main memory.▼
===Upgrade option===
In 1972 an upgrade option was announced "to provide the hardware necessary to operate in a virtual memory mode."<ref>{{cite newspaper|newspaper=Computerworld|date=August 15, 1973|page=17|title=First IBM DAT Box Installed|url=https://books.google.com/books?id=T3qky0Z-gc0C&pg=PA17#v=onepage&q&f=false}}</ref>
 
Another signs of not being "the real 370 line" is that the main storage in 3155 was not monolithic, it was using the older type of ferrite [[core storage]]. The 3360 storage unit could have 256 or 512&nbsp;KB of storage, each 3155 could have one to four 3360 units attached. Also, the microcode in 3155 was "hardwired" while later 370 systems loaded the microcode from a [[floppy disk]], enabling easy upgrades. The 3155 also had very limited error logging capability and used an [[IBM 3215]] typewriter console.
Unlike the [[IBM System/370 Model 145]], which as early as June 1971 could have virtual memory capability added to it with a simple [[microcode]] update from a floppy disk, the Model 155 and Model 165 needed expensive hardware additions - $200,000 for the 155 and $400,000 for the 165 - to add virtual memory capability, and even this had to
▲wait until 1972, at which time their upgraded 155 was known as an IBM System/370 Model 155-II.<ref>{{cite journal | author = A. Padegs | title = System/360 and Beyond | journal = IBM Journal of Research & Development | volume = 25 | issue = 5 | pages = 377–390 |date=September 1981 | publisher = IBM | doi = 10.1147/rd.255.0377}} &ndash; tables include model characteristics (Table 1) and announcement/shipment dates (Table 2). The S/370-155-II and -165-II are listed under the former but not the latter, because the upgraded systems were not formally announced as separate models. The "System/370 Advanced Function" announcement, including the -158 and -168, was the main public event.</ref>
 
==Physical memoryChannels==
Channel 0 was a byte multiplexor channel, channel 1 to 5 were block multiplexor channels. Channel 0 and 1 were standard, channel 2 to 5 were optional upgrades.
▲Although the joint 155/165 announcement<ref name=IBMarc.165/> did not have the word virtual, there were multiple references to (physical) memory, storage (both main memory and disk storage), and [[cache memory]] under the name "buffer".
 
==Operating systems==
The 370/155 supported both [[DOS/360 and successors|DOS/360]] and [[OS/360 and successors|OS/360]].<ref name=IBMarc.155 /> Being members of the System/370 family, the Model 155 and Model 165 were compatible with each other. Lacking virtual memory support, neither machine, as announced, could run a virtual memory operating system.
 
A 370/155 upgraded to a 370/155-II, with support for virtual memory added, supported [[DOS/VS]] (DOS/360 with virtual storage), [[OS/VS1]] ([[OS/360 and successors#OS/MFT|OS/360 MFT]] with virtual storage), OS/VS2 Release 1 ([[OS/360 and successors#OS/MVT|OS/360 MVT]] with virtual storage), termed [[OS/VS2 (SVS)|SVS]] (Single Virtual Storage), and Release 2, termed [[MVS]] (Multiple Virtual Storage), and [[VM (operating system)|VM/370]].
▲The 155 had seven main memory choices, ranging from 256K to 2 MB; the 165: five possibilities, from 512K to 3 MB. Both models were described as having "a very high-performance buffer storage backed by a large" main memory.
 
==See also==
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{{DEFAULTSORT:IBM System 370 Model 155}}
[[Category:IBM computers]]
[[Category:IBM System/360 mainframe line]]
[[Category:Computer-related introductions in 1970]]
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