Under construction! pictures and more materials will be added.

The goals of this project are:

1) Learn, understand, document the design of ORDVAC.
2) Build a portion of ORDVAC and interface it with computer


Why? Well, I love electron tubes. I love computers. I love history. You got the idea.



I began to look into a lot of 1st generation computers. Since I am a student at U of I, it is natural to pay attention to ILLIAC I. Surprisingly very little have survived regarding the design of the hardware. It is very hard to find information on tube-based logic circuits.

One day, out of whim, I sent e-mail to Prof. Sylvian Ray whom I have taken a course from long time ago. He is origianlly an EE guy, but has been into AI for long time now. It turned out, he was actually at the Aberdeen Probing Ground (BRL) where ENIAC, EDVAC and ORDVAC were operating. He was in charge of taking care of ORDVAC, a clone of ILLIAC I, designed and manufactured by the U of I. (They were not exactly clones, but close enough)

Prof. Ray had a copy of ORDVAC manuals which contain circuit diagrams and detailed operational princicples. I borrowed them and eventually made PDF files. Here they are: ORDVAC Manual Volume I, ORDVAC Manual Volume II.

The first polished design of Von Neumann computer was so-called IAS machine. At the Institute for Advanced Studies at Princeton, John von Neumann and colleagues designed it. It became operational in 1952. Based on their design many others made similar computers. U of I started building two in 1949 and completed ORDVAC in 1951. In 1952, it was delivered to BRL where ENIAC and EDVAC were installed. ILLIAC I was completed in 1952. So ORDVAC is one of the fisrt IAS machines.

ORDVAC went through a series of make-over in the subsequent years until its retirement in mid 60s. One of the most significant change was the memory. It originally had Williams tube based memory system which was better than EDVAC's mercury delay line but still not very reliable. The BRL engineers "upgraded" it to the magnetic core memory. It took less space and power, and much more reliable. They also transisterized the arithmetic unit.

The electron tube-based computers were not so reliable. If you "cold" start the computer, there are 25 to 50% chance of operating correctly.