Editing IBM System/360 (section)

===Models===
IBM initially announced a series of six computers and forty common peripherals. IBM eventually delivered fourteen models, including rare one-off models for [[NASA]]. The least expensive model was the [[IBM System/360 Model 20|Model 20]] with as little as 4096 bytes of [[magnetic-core memory|core memory]], eight 16-bit registers instead of the sixteen 32-bit registers of other System/360 models, and an [[instruction set]] that was a subset of that used by the rest of the range.

The initial announcement in 1964 included Models [[IBM System/360 Model 30|30]], [[IBM System/360 Model 40|40]], [[IBM System/360 Model 50|50]], 60, 62, and 70. The first three were low- to middle-range systems aimed at the [[IBM 1400 series]] market. All three first shipped in mid-1965. The last three, intended to replace the [[IBM 700/7000 series|7000 series]] machines, never shipped and were replaced with the [[IBM System/360 Model 65|65]] and [[IBM System/360 Model 75|75]], which were first delivered in November 1965, and January 1966, respectively.

Later additions to the low-end included models [[IBM System/360 Model 20|20]] (1966, mentioned above), [[IBM System/360 Model 22|22]] (1971), and 25 (1968). The Model 20 had several sub-models; sub-model 5 was at the higher end of the model. The Model 22 was a recycled Model 30 with minor limitations: a smaller maximum memory configuration, and slower I/O channels, which limited it to slower and lower-capacity disk and tape devices than on the 30.

The [[IBM System/360 Model 44|Model 44]] (1966) was a specialized model, designed for scientific computing and for real-time computing and process control, featuring some additional instructions, and with all storage-to-storage instructions and five other complex instructions eliminated.
[[File:360-91-panel.jpg|thumb|220px|[[IBM System/360 Model 91]] operator's [[system console|console]] at NASA, sometime in the late 1960s.]]
[[File:IBM magnetic core.jpg|thumb|right|220px|Magnetic-core memory, probably from a 360]]

A succession of high-end machines included the [[IBM System/360-67|Model 67]] (1966, mentioned below, briefly anticipated as the 64 and 66<ref>{{cite magazine|url=https://apps.dtic.mil/sti/citations/AD0694645|title=System/360 Time Sharing Computers|magazine=DIGITAL COMPUTER NEWSLETTER|volume=17|issue=3|publisher=Office of Naval Research, Mathematical Sciences Division|date=July 1965|pages=5–6}}</ref>), 85 (1969), [[IBM System/360 Model 91|91]] (1967, anticipated as the 92), 95 (1968), and 195 (1971). The 85 design was intermediate between the System/360 line and the follow-on [[IBM System/370|System/370]] and was the basis for the 370/165. There was a System/370 version of the 195, but it did not include Dynamic Address Translation.

The implementations differed substantially, using different native data path widths, presence or absence of microcode, yet were extremely compatible. Except where specifically documented, the models were architecturally compatible. The [[IBM System/360 Model 91|91]], for example, was designed for scientific computing and provided [[Out-of-order execution|out-of-order instruction execution]] (and could yield "imprecise interrupts" if a program trap occurred while several instructions were being read), but lacked the decimal instruction set used in commercial applications. New features could be added without violating architectural definitions: the 65 had a dual-processor version (M65MP) with extensions for inter-CPU signalling; the 85 introduced cache memory. Models 44, 75, 91, 95, and 195 were implemented with hardwired logic, rather than microcoded as all other models.

The [[IBM System/360 Model 67|Model 67]], announced in August 1965, was the first production IBM system to offer [[Virtual memory|dynamic address translation]] (virtual memory) hardware to support [[time-sharing]]. "DAT" is now more commonly referred to as an [[memory management unit|MMU]]. An experimental one-off unit was built based on a model 40. Before the 67, IBM had announced models 64 and 66, DAT versions of the 60 and 62, but they were almost immediately replaced with the 67 at the same time that the 60 and 62 were replaced with the 65. DAT hardware would reappear in the [[S/370]] series in 1972, though it was initially absent from the series. Like its close relative, the 65, the 67 also offered dual CPUs.

IBM stopped marketing all System/360 models by the end of 1977.<ref>{{cite web
 | url       = http://www.vm.ibm.com/devpages/jelliott/pdfs/zhistory.pdf
 | title     = IBM Mainframes – 45+ Years of Evolution
 | last      = Elliott
 | first     = Jim
 | publisher = IBM Canada Ltd.
 | page      = 17
 | year      = 2010}} shows the announcement, ship and withdrawal dates for all S/360 models other than the transient models 64 and 66</ref>