Talk:IBM 1620

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Contents 1 100,000 digit 1620 2 Clock or memory cycle speed 3 Inexpensive ??? 4 Cadet vs. Stretch 5 CADET joke 6 Multi-level Indirect Addressing

[edit] 100,000 digit 1620

I was told by a CAI (computer aided instruction) author in 1969 that one 100,000 digit 1620 had been constructed. The primary modification to the machine was the enabling of the 80,000 digit circuit in the memory address registers.

Well, I wouldn't be entirely surprized if ONE was customized for a specific customer, many even had custom instructions or I/O devices that a customer requested. However IBM destroyed all their customer records on the machine at some point and this is impossible to prove now. It would also require an extra IBM 1623 (Model I), IBM 1625 (Model II) or similar Memory unit to house the additional 40,000 digits and support electronics. The Computer History Museum's IBM 1620 restoration project tried to get copies of any records from the IBM archives.

If you have any idea where this "extended memory" 1620 was and if it was a Model I or a Model II it would be very helpful. -- RTC 18:13, 29 Oct 2003 (UTC)

As the standard 1620 MARS Core plane did not have an 80,000 bit (there was no bit to "enable"), this modification would have required a custom MARS Core plane as well as an extra flip-flop in the MAR. -- RTC 00:10, 26 Jan 2004 (UTC)

[edit] Clock or memory cycle speed

Hi, great article for the computer history enthusiast! Does someone know the clock or memory cycle speed, or relevant equivalent characteristic, of the 1620? --Wernher 07:28, 22 Nov 2003 (UTC)

I was on the team that restored a Model I to operation and have full schematics.... read the articles on the individual models as things are different! -- RTC 07:38, 22 Nov 2003 (UTC)

Oops, sorry, I didn't notice the separate Model I article (misunderstood it to be part of the 1620 main article). Now, however, I am enlightened :-) --Wernher 08:24, 22 Nov 2003 (UTC)

Good question. My vague recollection is that the clock speed was on the order of about 10 microseconds. Someone should look up the facts and add summary speed info to the main 1620 article. 69.87.204.125 20:35, 16 September 2006 (UTC)

[edit] Inexpensive ???

The word "inexpensive" in the opening § should be qualified/explained or else be set in quotes, I think, since I guess we're not exactly talking small change here :-) --Wernher 07:28, 22 Nov 2003 (UTC)

Inexpensive compared to other IBM scientific computers (e.g. IBM 7090) of the time. Read the Model I article. -- RTC 07:38, 22 Nov 2003 (UTC)

Cost information should be added; it was relatively small and cheap, which was very important in context. 69.87.204.125 20:57, 16 September 2006 (UTC)

[edit] Cadet vs. Stretch

When I interviewed for my job with IBM at the Mohansic Advanced System Development Division lab in Yorktown Heights, New York one of the people who I talked to was an engineer named Jack Gibson.

As we chatted, I mentioned that the 1620 was the computer I first learned to program. He told me that the 1620 was near and dear to his heart. He said that he had worked in the project office for both the 1620 and the IBM 7030 a.k.a. Stretch.

The budget approach to these two machines was amazingly different. He said that when an engineer on the 7030 approached the project office with the need to add a gate to the machine, it got some scrutiny but was approved. In those days, the term 'gate' on an IBM computer didn't mean a simple logic circuit, it meant a large swinging frame which held multiple circuit cards and represented a sizable cost.

On the 1620 however, the addition of simple and inexpensive components like pull-up resistors had to be rigidly justified and often the engineer was told to redesign and find a cheaper alternative.

That interview was the first time I ever heard the CADET=Can't Add Doesn't Even Try line.

Yes, I got the job, and I'm still with IBM some 30 years later.

On the 1620 those resistors would most likely have been pull-down resistors, as SDTRL logic used PNP transistors to pull their output to ground and resistors to pull-down to -6V – -12V. -- RTC 09:25, 21 Jan 2005 (UTC)

[edit] CADET joke

That C.A.D.E.T. - now I think that acronym ought to be in the article. I also knew and worked with one of the design team in 1964, and was told the "Can't Add Doesn't Even Try' term. --Dumarest 21:22, 4 July 2006 (UTC)

The internal code name CADET already appears in the article. There are three known interpretations of it:

"The internal code name CADET was selected for the machine. One of the developers says that this stood for "Computer with ADvanced Economic Technology", however others recall it as simply being one half of "SPACE - CADET", where SPACE was the internal code name of the IBM 1401 machine, also then under development."

...

"Following transfer to San Jose, someone there jokingly suggested that the code name CADET actually stood for "Can't Add, Doesn't Even Try", referring to the use of addition tables in memory rather than dedicated addition circuitry. This stuck and became very well known among the user community."

-- RTC 20:10, 5 July 2006 (UTC)

As on my page, the point is that the 'joke' is NOT in the actual article - it was, but removed - I think it belongs in the actual article, it is a valid piece of history, and 'encyclopedic'. --Dumarest 20:16, 6 July 2006 (UTC)

Well, for what it is worth I added a redundant reference to the CADET joke in the introduction. If such duplication is needed, then that is were it belongs, not out of time sequence in the development history section, as it had been added before. It has always been in the development history section, in the appropriate time sequence. -- RTC 02:46, 7 July 2006 (UTC)

I blush - this time I used a search to find it, and there it was [in the older version that I first looked at]. On beyond where the 'SPACE-CADET' term was, later in the history. I spoke without full knowledge when I started this thread. --Dumarest 12:18, 9 July 2006 (UTC)

No problem. -- RTC 04:05, 10 July 2006 (UTC)

[edit] Multi-level Indirect Addressing

"In the least significant digit of 5-digit addresses it was set for indirect addressing."

My recollection is that this allowed for simple, obvious, n-level indirect addressing. If this is true, I think it is worth mentioning -- a neat feature. 69.87.204.125 21:02, 16 September 2006 (UTC)

Yes it was multi-level, you could even put it in an infinite indirect addressing loop. But on the Model I indirect addressing was an option, most Model I systems didn't have it. -- RTC 19:57, 17 September 2006 (UTC)