Talk:Harvard Mark I

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Arthur Lemay Harvard Class of 1959[edit]

In 1955 I was a student at Harvard and spent many hours in laboratory time programming the Univac I prototype, which was located immediately adjacent to the Harvard Mark I computer, and the later Mark II and other early vacuum tube computers.

The Mark I was enormously large and complex, and, at the time when I first saw it, it was running a code for designing lenses for military equipment. This computational task ran for weeks and weeks, and produced all of its results on a set of 10 Flexowriters (really just computer driven typewriters). The programs were not in memory, they were on giant rolls of thick paper the width of the IBM 80 column card. And, there were reading stations for multiple rolls. After watching it for an instant, anyone could grasp the concept of loops since the controls tranferred from one reading station to the other and the execution could be watched while in process. The programmers often applied paper patches on the paper rolls to fix program errors -- these were real patches, and of course the word "patch" is used to this day for temporary changes to any software.

Originally, the memory was implemented with a set of disks the size of saucers mounted on shafts, each with a cam to engage the disk in one of ten positions. The number of disks seemed enormous to me at the time. There was also a very small vacuum tube memory added much later, but the Mark I was really an electromechanical machine.

My fondest memory of early computing was when, one day, the lens program was done and the Laboratory staff set up a new problem for the Mark I to solve.

I watched as two graduate students entered constants into the memory: One was on a stepladder in front of a huge panel with 10-position butterfly switches. The other student yelled out 4, 6, 7, 2, 1, etc., and the first student on the stepladder set the switches for each digit in each memory constant. This took many hours to accomplish because all the constants needed to checked and verified. Then the paper tape programs were mounted and sequenced to their start positions. The next step was the process of actually transferring the fixed constants to disk-on-shaft memory.

There was a very large lever mounted inside the machine on what looked like a transmission box. The lever was quite long, giving good mechanical leverage, and the lever was up in the disengaged position -- withdrawing the cams and letting the disks spin freely on the shafts. The shafts were put in motion, at first giving a low-pitched mechanical humming sound, quieting down as the bearings came up to operating temperature. Then, the student brought the lever down a short way and we heard the most enormous clatter of the cams engaging the disks. Of course the inertia of accelerating the disks caused a strong backlash on the lever and one man could barely hold it. The lever was brought down further and the clatter got even louder and it seemed like the computer was shaking and the lever oscillated up and down violently. Then, suddenly -- total silence -- and the lever dropped home to the engaged position when all the disks on all the shafts were syncronized to the settings on the butterfly switches.

The dynamic memory was implemented in a large array of relays which actually had a very small capacity. This memory was initialized and the tapes commanded to read and execute the codes contained there. This computer ran the problem for weeks.

But, this was the world's first fully automatic computer, and it ran many problems in its lifetime. It is a pity that it no longer exists, but I saw some parts in Museums in Boston and Sunnyvale, California.

Arthur Lemay Harvard Class of 1959

Does anyone know what sort of problems the Mark I was created to solve? I heard it was made to calculate ballistic firing tables for artillery during the war, but I'd like to read that from an authoritative source. I've also never seen a ballistic firing table and wonder what they looked like.

"The History of Mathematical Tables from Sumer to Spreadsheets", ISBN 0198508417 refers to the Mark I as having cranked out 50 volumes of Bessel function tables among other things...--Billymac00 (talk) 02:58, 13 April 2010 (UTC)


"The main advantage of the Mark I was that it was fully automatic—it didn't need any human intervention once it started. It was the first fully automatic computer to be completed."

What exactly does this mean? This was Mark I's main advantage compare to what? I also don't see how the ABC, Eniac or Collosus are any "less automatic"?

"the beginning of the era of the modern computer"[2] and "the real dawn of the computer age".[3]

Really? Both of these statements seem odd - this machine is widely regarded as a dead-end, the last of its kind. The debate will rage always, but it moves between the ABC, Collosus and Eniac; the Mark I, and Z-1 for that matter, are always mentioned but generally commented on as not being "real" computers in the modern sense of the word.

Maury Markowitz (talk) 02:07, 23 January 2009 (UTC)

Bel Geddes[edit]

According to the Norman Bel Geddes article, he was involved in the design of this machine. 2fort5r (talk) 11:53, 14 July 2009 (UTC)

comey dy yuhu dh y d —Preceding unsigned comment added by (talk) 11:54, 30 October 2009 (UTC)

Insert non-formatted text here== Questions==

Who the hell is "Dr Camila Olmedo Mendez Zegarra"? —Preceding unsigned comment added by (talk) 09:09, 28 February 2010 (UTC)

Pleas do no put in expletives. That name was part of some vandalism stuck into the article. Dmcq (talk) 21:25, 3 September 2010 (UTC)

Heading text[edit]

why Howard Aiken named the harvard mark 1 as mark,if he can use the official name Automatic Sequence Controlled Calculator?

More in table[edit]

The table and "see also" sections are a bit redundant. And The IBM SSEC needs to go in the table. It was odd in using electronics to do the computation, but relays and tapes to store programs. Used BCD I think, and probably was Turing complete in theory? Ah, that is a separate template. Discussion belongs there.

W Nowicki (talk) 19:42, 23 April 2011 (UTC)


A bit misleading to say "Harvard" renamed it. Most modern sources now call it the "Harvard Mark I", even IBM uses both names. Also I wonder about the front panel. IBM had a history of doctoring photos to make their marketing look slick (ahead of their time?). But would need a source for this. W Nowicki (talk) 23:28, 23 April 2011 (UTC)

Additional Source[edit]

I was browsing through the Wikipedia article for the UNIVAC computer, and noticed that it contained a citation to a 1949 Popular Science article. This article referenced a 1944 Popular Science article, which I've posted the Google Books link above. I don't really have the time to incorporate this additional information into the Harvard Mark I Wikipedia article, but it seems like a fascinating read. For now, I've added the link to the external references section of the article, but if someone could incorporate the new information, that would be great.

Thanks! Jason Smith (talk) 01:13, 15 February 2012 (UTC)