Hannon S. Yourke


Curator’s Introduction


Hannon S. Yourke’s 30 year career with IBM began in 1955 when he joined the newly formed transistor circuits group in Poughkeepsie.  All IBM computers at the time were vacuum tube based, and the transistor group had been formed to investigate and develop the potential for transistors in future IBM products.  Mr. Yourke’s contributions were soon in coming and were to have a substantial impact on high performance computer circuitry for decades to follow.  He filed for patent 2,964,652 (Transistor Switchjng Circuits) in Nov 1956 – this patent, granted in December 1960, developed a set of transistor switching circuits in which the transistors were operated in a non-saturated manner.  This non-saturated operation of the transistors allowed for substantially faster switching speeds than was possible with the saturated circuitry common at the time.  The circuitry developed by Mr. Yourke was known initially as current steering logic, but was later called emitter coupled logic, or ECL.  This form of logic became the dominant circuitry for all high speed computer logic throughout the 1960s, 1970s and 1980s.


This Oral History will provide comments from Mr. Yourke regarding his early transistor work at IBM, and, in addition, a brief discussion and list of references will be included to document the development and use of ECL in the decades following Hannon’s original work and patent.


Yourke Historic Audio Recordings




Oral History – Hannon Yourke


Early Transistor Work at MIT

on Master’s Thesis before Joining IBM.

My thesis dealt with triggers, negative resistance flip flops using point contact transistors. This was in 1953 and 1954, at the Cambridge (Massachusetts) Air Force Research Center, where I was a co-op student from MIT.  There were only point contact transistors available; Shockley was   just inventing the junction type then.  I was the junior man in the lab, and didn’t actually make any transistors, but used them in circuits.  I think there were a couple of guys there in the lab putting some together.    I didn’t need many transistors for my work, which involved flip flops. My (thesis) professor was named Adler, who I thought made a great contribution by developing an equivalent circuit for a transistor, which I found very useful in describing the operation of a transistor. 


I graduated from MIT in June 1954 with simultaneous Bachelor and Master degrees, paid for by the GI Bill, and started my career at Norden Laboratories, where I worked on microwave circuits and had a patent on a rotary joint.  They were located in White Plains, NY, and my work with them was from June 1954 until I left in July 1955.  Then I went to IBM and joined their transistor circuits group in Poughkeepsie (Research).  Joe Logue was heading the group and the person I reported to was Bob Henle.  They were working with saturated circuits at the time, but I had already been working on non-saturated techniques, through my thesis.  So, I started at IBM in July 1955 and my first notebook entries on the transistor current steering logic was in August 1956, about one year later.   

Go To Yourke Oral History, Page 2


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