Talk:IBM System/4 Pi

Possible merger
I've been making some incremental edits to both IBM System/4 Pi and IBM AP-101. I'm thinking it might be better to merge them, at least in the short term, as there is quite a bit of overlap. Thoughts? --mikeu talk 23:15, 27 October 2013 (UTC)
 * I agree there's a lot of overlap which could easily be merged. -- Cy be r XR ef ☎ 04:18, 8 February 2014 (UTC)

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360 or not? Comment
In the intro it is stated the computer doesn't really share System/360 architecture, while in the rest of the article it is stated it does. Since the former statement is unsourced and the others are properly referenced, I'd say proper 360 heritage is more likely... --Arny (talk) 09:00, 23 August 2017 (UTC)


 * I'm not sure that all members of the 4Pi series are 360 derived. The early Model EP is described in 1967 as using "an instruction subset of the IBM System/360" but the TC and CP models are not. The AP-101 was an improved version of the AP-1 which was derived from the EP which was based on the 360.


 * "The 4Pi AP-1's advantages lay in its history and architecture. Already used in aircraft applications, it was also related to the 4Pi computers on Skylab, which were members of the same architectural family as the IBM System 360 mainframe series. Since the instruction set for the AP-1 and 360 were very similar, experienced 360 programmers would need little retraining." and "The AP-101 has the same type of registers and architecture used in the IBM System 360 and throughout the 4Pi series." Computers in Spaceflight: The NASA Experience by James E. Tomayko, March 1988. NASA Contractor Report 182505.


 * NASA used IBM 360/75 mainframes that were "compatible" with the AP101 as a development environment. These had specialized interfaces to connect to flight hardware. It is very likely that these may have needed custom user writable microcode to emulate the flight computer. I have not been able to locate a reference that describes this in detail.


 * Even for these later models it unclear to me how similar these really are to the 360. The AP-101S can be configured for either the IBM Multipurpose Midline Processor (MMP) ISA (the only mode in the Shuttle AP-101B) or MIL-STD-1750A (used in some USAF aircraft.) Depending on which of the modes it is operating in the computer might function more or less like a 360. --mikeu talk 20:26, 12 December 2017 (UTC)
 * Does that mode configuration correspond to distinct microprogrammable instruction sets ?  What can we say about the different microprograms ? - Rod57 (talk) 20:00, 24 November 2018 (UTC)

AP not listed under Models
Was the AP after the reference used for the Models section ? Can we add it ? - Rod57 (talk) 01:43, 25 November 2018 (UTC)


 * Text about AP existed before adding the references (AP is a later model), I think it could be moved to Models if it's not too long, because there is even more models (ML-1, CC-1/2, SP-1 and possibly others): (table lower parts: search "Logic 5 Gates" and "Price/Performance"), ,
 * Related to ML-1, but requires buying/subscription:, direct link:
 * Related to AP-101: introduced in 1970, ; trivia: , --MarMi wiki (talk) 02:35, 18 December 2018 (UTC)