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Fascinating article. Would love to know what the thinking is behind the CCS instruction - what sort of problem does it solve? What would be a modern (C, say) equivalent contruction? GRAHAMUK 04:51, 2 Sep 2003 (UTC)
The "single" and "double" precision mentioned in the article links to IEEE definitions, but surely the author meant one or two of the 15/16-bit words the machine used? --Anonymous, 21 Apr 2004
In this chapter there is a link to a picture and also to a diagram of the DSKY. The two do not match. [1] has there indicators:
+------------+------------+ |UPLINK ACTY | TEMP | +------------+------------+ | AUTO |GIMBAL LOCK | +------------+------------+ | HOLD | PROG | +------------+------------+ | FREE | RESTART | +------------+------------+ | NO ATT | TRACKER | +------------+------------+ | STBY | [ ] | +------------+------------+ | KEY REL | OPR ERR | +------------+------------+
Compare that to
+------------+------------+ |UPLINK ACTY | TEMP | +------------+------------+ | NO ATT |GIMBAL LOCK | +------------+------------+ | HOLD | PROG | +------------+------------+ | KEY REL | RESTART | +------------+------------+ | OPR ERR | TRACKER | +------------+------------+ | [ ] | ALT | +------------+------------+ | [ ] | VEL | +------------+------------+
For contemporary readers who may not have been alive at the time, or who may not be intimately familiar with computer architecture, the Apollo Guidance Computer could use a comparison to later well-known computers or calculators. For example, how would it compare to the HP-65 programmable calculator, or a personal computer, such as the Apple II or IBM PC that came a decade or so later? Quicksilver 02:13, 11 November 2005 (UTC)
This is a fascinating article, but I find myself wondering what exactly this computer was used for on its missions. The article says that it was used to "collect and provide flight information, and to automatically control all of the navigational functions of the Apollo spacecraft," but I'd like to see a more detailed explanation than that.
For example, what kinds of "flight information" were collected? What were the "navigational functions" of the spacecraft? Presumably the computer did not "fly the spacecraft" in a completely automatic manner. I would be interested to know more about in what way the computer was used by the astronauts to operate the craft.
DrDeke 15:29, 8 March 2006 (UTC)
The article still suffers from a certain lack of focus in the introduction. A naive reader could be forgiven for thinking that this was an article about embedded systems, as the lede leads with "The Apollo Guidance Computer (AGC) was the first recognizably modern embedded system". The focus at this point should be on what the AGC was and did. I'm looking at the article now (I'm in the middle of rereading Mike Collins's book "Carrying the Fire" (still my favourite after 30 some years, even with the advent of Chaikin's etc), Aldrin's "Men from Earth" and Don Eyles's "Tales from the Lunar Module Guidance Computer", hence the interest) and will make some change to effect this in the next hour or so. Lissajous (talk) 14:17, 27 August 2009 (UTC)
We should probably add more information about the decision to use ICs in the AGC rather than discrete transistors. I've added links to some documents on the klabs.org site discussing this decision and it would appear to have been highly contentious at the time but extremely sensible in hindsight. MarkGrant 02:11, 9 July 2006 (UTC)
It is unclear that the AGC was the first computer to use integrated circuits. HP's 2116A (HP_2100), introduced in 1966 the same year as the AGC, may or may not hold that title. The 2116A was of course much larger at around 230 pounds, but it was a full general purpose computer, not a specialized controller. Badtux (talk) 18:23, 21 July 2019 (UTC)
This is an excellent article, but I question the assertion that it was the program alarms that caused Neil Armstrong to go to manual control of the Apollo 11 landing. Is there a source? As far as I know, all of the astronauts went to manual control during lunar landings, and I've never seen Armstrong's decision singled out like this before. --MLilburne 09:16, 13 July 2006 (UTC)
In First on the Moon', (Little Brown, 1970) Armstrong says he took manual control when he realized they were about to land in a boulder field. The alarm problems were an issue becaused they distracted him from looking out the window and following landmarks, but it was the realization that they were heading for a poor landing spot that caused him to take over the throtle ontrol so he could slow the rate of decent and allow more time at a higher altitude where he cold select a better spot.--agr 15:00, 8 December 2006 (UTC)
The 1201 and 1202 alarms were caused by too many events from the Rendezvous Radar (part of the Abort Guidance System) which was attempting to track the CSM in case the abort switch was pressed during decent. This Rendezvous Radar was disabled during decent in subsequent missions which is why you never hear about it after Apollo 11. --Neilrieck 03:04, 10 February 2007 (UTC)
Somebody needs to correct this. It can't have been 5 to 10 kW reduction. More like tens of Watts.
Presumably it's the same. The text has been corrected already to read W not kW.--agr 14:44, 8 December 2006 (UTC)
The article says, that the standby mode was never used. Is this really true? I can't believe this. What about Apollo 13? —Preceding unsigned comment added by 89.27.200.16 (talk) 12:37, 24 July 2009 (UTC)
The photo is nice but gives no indication of scale. Could anyone add to the description section indications of Power usage and Physical dimensions? Garrie 03:01, 12 December 2006 (UTC)
I added the technical and generalize tags. This page is far too technical. This is obviously an amazingly important technology, but I don't know that describing clock cycles, circuit design, and other technical specifications are the best ways to convey it. Can we get more about the historical context (state of IC computers in the era), advancements that the computer made that can still be seen in modern computers, how the computer affected or resolved missions-in-flight (ie Apollo 13)?Madcoverboy 16:02, 11 March 2007 (UTC)
The description section says, The Apollo flight computer was the first to use integrated circuits (ICs), and then later on, The decision to use a single IC design throughout the AGC avoided problems that plagued another early IC computer design, the Minuteman II guidance computer. If there was an earlier design, how could this be the first? -- RoySmith (talk) 20:28, 26 June 2007 (UTC)
Looks to me like it was the Minuteman II that was the first successful all-digital flight computer [2], the first MM2 test flight occurred in September 1964. [3] Banjodog (talk) 05:53, 27 January 2009 (UTC)
Can you tell whether it is this Apollo Guidance Computer (AGC) that displayed an "error 1202" during Apollo 11 landing on the moon and forced Armstrong to moonland manually ?
The MIT AGC Project link is effectively dead --
The Burndy Library has moved to the Huntington Library, Art Collections, and Botanical Gardens in San Marino, California. The Dibner Institute, formerly on the MIT campus, is now closed. Information regarding the Burndy Library and Dibner Fellowships may now be found at http://huntington.org/burndy.htm. Inquiries may be sent to publicinformation@huntington.org.
Some of the material is archived at http://authors.library.caltech.edu/5456/, but I haven't tracked down all of the items from the external links yet. Autopilot (talk) 00:13, 5 March 2008 (UTC)
Are there any examples of how the verb / noun command inputs worked? I can see the codes in the picture of the side panel, but its not clear what they are for or how they are used.
-Bill —Preceding unsigned comment added by 75.180.8.80 (talk) 12:10, 26 July 2009 (UTC)
Disclaimer: I didn't introduce the kibi/mibi nomenclature.
Has there been prior discussion on the units used in the article? A recent edit has removed references to KIBI and MIBI (see kibibyte) and replaced them with the more widely used (but arguably misleading) "kilo" and "mega". The original references were in line with the (not widely used) IEC standard for referring to powers of 2 (binary). I was myself tempted to make the same change, but left alone on the basis that there might have been good reason/prior consensus, and moreover the IEC designations are in some small way more precise.
Is there good argument for not using the kibi/mibi nomenclature? Lissajous (talk) 08:40, 4 September 2009 (UTC)
Lissajous (talk) 18:37, 4 September 2009 (UTC)
I'm in no great hurry, but at some time I'd like to move the focus of the article to be on the Block II design (which actually flew the manned missions), with the Block I taking a lesser role. At present the text describes the Block I by default, with references to changes for the block II made later. The design history is interesting, and the evolution from Block I to Block II is important, but the design of interest is in fact the Block-II version. Are there good reasons for not doing this? Lissajous (talk) 05:30, 11 October 2009 (UTC)
These links actually seem to be working now. Added 'nb.' on size of downloads. --220.101.28.25 (talk) 11:48, 31 October 2009 (UTC)
"The software could be overwritten by the astronauts using the DSKY interface. As as done on Apollo 14." - this seems rather dubious to me as the software was in fixed core memory, and the only explanation I've found of AGC hacks on Apollo 14 is this:
http://www.ibiblio.org/apollo/#Solution_to_the_Apollo_14_Final_Exam
So in that case it would appear that the astronauts were changing variables in the erasable memory rather than code.
I'm sure I do remember a mission installing a software 'patch' in erasable memory but can't find any reference to it now. And that's still not really 'overwriting' the software. Mark Grant (talk) 05:17, 15 September 2010 (UTC)
At the top of the article it mentions that the dimensions of the AGC are 24" x 12.5", however from the pictures it looks more squarish, and I recall it being more like 8" x 8". Is there a source to confirm dimensions? Or maybe I am thinking of just the DSKY part of it? Logicman1966 (talk) 23:48, 9 February 2011 (UTC)
> Block II had 32 kilowords of fixed memory and 4 kilowords of erasable memory.
I'd like to explain this in terms an ordinary person will understand - would it be fair to say: "approximately as much memory as a Comodore 64" ?
Regards, Ben Aveling 10:57, 7 October 2011 (UTC)
This is kinda confusing. So according to what it says now, it sounds as if full on used 70W and standby used 65W or 60W -- and I'm not sure that's correct. Also, can we get an inline reference there? 31.16.108.201 (talk) 23:38, 26 February 2012 (UTC)
In the 1960's I was an engineer who worked on the AGC at Raytheon. I noticed four minor factual errors:
1. There were actually 2 different integrated circuits in the AGC. As stated, one was the dual RTL 3-input nor gates used for the logic (made by Fairchild). In addition the menory used an integrated circuit sense amplifier (made by Norden).
2. The packaging of the ICs was not in flat packs, but metal TO-5 can-style packages (I forget the number of leads). I believe this was done for cooling reasons. The AGC was conduction cooled (no air in space) and the individual modules had magnesium headers with holes for the TO-5 cans, resistors, and other components.
3. Although wire wrap was used in the backplane connections (for module-to-module connections), within the (epoxy) potted modules the interconnections were welded wire. (Solder connections were viewed as too unreliable).
4. I challange the photo of the erasable core memory. The erasable memory was not built of individual planes as pictured, but was a "folded" design which was also potted to form a module like the others, but in a "silastic" type material since the epoxy was too rigid and the cores couldn't stand any compressive force. Interestingly, each core had 4 tiny magnet wires threading through it. The requirement of no solder connections also applied to those magnet wires each of which needed to thread several hundred tiny cores. In the process of manufacturing the "folded" stack, sometimes cores needed to be replaced (because they were defective), which meant painstakingly removing and replacing the 4 wires involved. In commercial memories where solder splices are allowed it's easy, but for the AGC memory the 4 wires needed to be replaced and re-strung. — Preceding unsigned comment added by 72.28.170.2 (talk) 19:01, 8 July 2012 (UTC)
Found this from page 95 of the book "The Apollo Guidance Computer: Architecture and Operation, ed:Frank OBrien" "Communicationg with the outside world :the IO system , The EDRUPT instruction"
It appears to explain how the EDRUPT Instruction was used. For disabling interupt, and appears to have been used for implimenting self diagnostic tests.
When EDRUPT is run, all other intrupts are disabled, and ZRUPT register loaded with value of Z (program counter) , and during the LM autopilot , code for terminating the DAP cycle is run, then RESUME instructoin is run at the end to re-enable interupts.
so the like (not exact word-to-word, just extracting how the Instruction is __supposed_ to work) Not verified on the AGC emu yet, but this appears reasonable. 27.253.192.65 (talk) 15:21, 3 April 2013 (UTC)
The wikipedia article claims there are only 11 opcodes. However two of the links in the external section clearly contradict that:
Margaret Hamilton has become somewhat of an icon for women in STEM in the past year or so, which is all well and good, but it has caused some dubious claims about her accomplishments to creep in. She is often called, without qualification, the leader of Apollo software design. This was not a responsibility she held from the beginning of the program, rather only becoming the leader for command module software sometime after Apollo 8, and gaining responsibility for LM software later still. Major architectural elements she has been given credit for, namely the virtual machine interpreter and the executive/waitlist system were not her creations. The virtual machine was designed by Hugh Blair-Smith. The executive/waitlist system was designed by J. Halcombe Laning and Richard Battin, based on a paper they wrote in 1956 and their experience with the WHIRLWIND machine. Hamilton certainly worked on implementing and applying these ideas, but there is no evidence that she originated these or similarly influential concepts. The main idea she originated, "Higher-Order Systems" was dead-on-arrival in academia [[4]] and industry [[5]]. HOS seems to bear some relation to the work of Dijkstra and Hoare that preceded it as well as systems like coq or Haskell's Arrows that came later, but neither building on the former nor influencing the latter.
The idea that she coined the term "software engineering" is possible, but dubious. When asked directly about it, she said only that she "began to use"[6] the term, not that she began its use. The most widely recognized confirmed use of the term was in a 1965 letter by the president of the ACM, when Hamilton was 27 years old and not yet prominent in the Draper lab. Douglas T. Ross claims to have been using it as much as a decade before that, which Hamilton likely would have been exposed to while they both worked on the SAGE system. As eventual team leader, there's no doubt that Hamilton was involved in industrial aspects of software engineering like configuration management and schedule prediction. However, these things were quite notoriously imposed on the Draper lab by Bill Tindall around the time of Apollo 1. A sort of mythology has built up that software at that time was mostly done by women because it was denigrated by the male hardware engineers, but this doesn't really fit the facts. It conflates the kind of work Hamilton did with the rope memory weavers, who were seen as akin to telephone operators. Hamilton was among a tiny minority of women actually writing software at that time. It's true electrical hardware engineers tended to be dismissive of the challenges of software, but this was not a gender-based divide. Male computer scientists had been contending with it just as much as the few female ones for a decade by the time Hamilton began to work on Apollo. Software design and quality assurance became a program priority driven top-down by George C. Mueller and Bill Tindall, not something practiced surreptitiously and unappreciated. Rhoark (talk) 23:32, 4 June 2015 (UTC)
Taken together, I think this thoroughly establishes that however invaluable Hamilton's contributions were to the program, the interpreter could not possibly have been developed under Hamilton's direction, and it's extremely dubious that she influenced the interpreter or executive design in any significant way. Rhoark (talk) 03:46, 17 October 2015 (UTC)
In what ways is the AGC4 Memo #9, Block II Instructions (listed as an external link), infamous? Were there significant errors in the documentation?69.69.101.185 (talk) 21:36, 30 November 2017 (UTC)
"So the (in)famous Memo #9, simply listing the instructions and what they did, was enough for the people that mattered, and not enough for the people who didn't matter."
--89.25.210.104 (talk) 19:25, 5 April 2018 (UTC)
1959 - Mod 1A construction started
1960 - Construction of Mod 1B started, Mod 1A abandoned
1961 - Mod 1B completed
1962 - Mod 3C built, modified and completed into AGC3
1963 - AGC4
1964 - AGC5, AGC6
1965 - AGC7
Sources:
[14]:
3. Ramon L. Alonso et al., A Digital Control Computer Developmental Model 1B (1962, 12 Mbytes).
15. Hugh Blair-Smith, Annotations for Eldon Hall's book, Journey to the Moon: The History of the Apollo Guidance Computer (1997) ([15])
38. Eldon C Hall, MIT's Role in Project Apollo, Vol. III: Computer Subsystem (1972, 11 Mbytes).
[16], [17] (Additional materials) — Preceding unsigned comment added by 89.25.210.104 (talk) 18:48, 5 April 2018 (UTC)
[18]: Includes a picture of AGC4. — Preceding unsigned comment added by Iandiver (talk • contribs) 18:06, 27 May 2023 (UTC)
The pink/peach alloy used for the case - was it magnesium-aluminium - as stated by WSJ [19] ? - Rod57 (talk) 00:12, 16 September 2019 (UTC)
I tried to find this information in the article, but couldn't find it. Obviously there must have been two AGCs for every manned mission to the moon, but how many were tested before / flown on unmanned missions / used for something else later? And those few the article mentions that were used for later projects, were they surplus left over from the Apollo program, or did Raytheon continue to build some more specifically? --BjKa (talk) 19:13, 14 April 2020 (UTC)
For anyone interested in the AGC in general, or any detail of its workings and operation, I can highly recommend the videos of CuriousMarc, documenting a restoration of a privately owned AGC to working condition. --BjKa (talk) 19:13, 14 April 2020 (UTC)
the list of registers in this article is incomplete. for a more complete list of registers see Appendix C in the book: "The Apollo Guidance Computer: Architecture and Operation" by Frank O'Brien. ISBN: 1441908773, 9781441908773 — Preceding unsigned comment added by 61.69.177.79 (talk) 07:10, 6 December 2020 (UTC)
I raised this issue in August 2023 since welding seemed wrong to me. I received the following note on my talk page:
The relevant paragraph I added is:
So surprisingly as it seems welded, not soldered is the correct term. Please don't revert unless you have citable evidence to the contrary. Martin of Sheffield (talk) 10:57, 21 December 2023 (UTC)
References