I'm rather interested in the history of eletrical engineering, and I've seen some discussion here and there about the origin of the names of the various flip flop circuits. Some time ago I took part in one such discussion here: Understanding D flip flop function - what this thing does, and became so interested on the subject that I purchased an early textbook from 1957, which supposedly is the first university level textbook where flip-flops are discussed.

I promised to report my findings, and I'll do so below. But sadly it didn't answer all my questions. It seems that using flip flops was already an established tradition in 1957 and the book doesn't discuss any history. So please answer if you have any info on the subject.

So I am looking for references that predate 1957. I am also interested in the origin of the characters J and K in a JK flip-flop, in case someone would be able to verify or clarify the answer given in What is the meaning of JK flip flop's J and K ?.


3 Answers 3


Montgomery Phister's textbook "Logical design of digital computers" from 1958 (written in 1957) introduces the D flip-flop as "the delay memory element".

The D Flip-Flop

This doesn't prove anything but it suggests that already in 1957, at least, there was tradition to suggest that the D means "delay".

As a side-note to put things into historical perspective, here's a schematic for a flip-flop from the same book, using radio tubes and 200 volt anode voltage.

flip-flop made of radio tubes

  • 8
    \$\begingroup\$ I always thought "D" input on a D flop (or many other circuits) meant "data"; the term "delay" refers to the fact that the memory element unconditionally grabs the state from one bit-time before. Note that although the circuit shown includes a pair of cross-coupled triodes, it's actually using a form of dynamic logic (notice the capacitors on the inputs). \$\endgroup\$
    – supercat
    Jan 14, 2015 at 20:19
  • \$\begingroup\$ @supercat indeed that pulse is also reflected in the text. But actually, Phister's most important influence might have been that he was an early advocate of synchronous design, the prevalent design methodology of today. In his book's preface he writes that "A great many very successful computers" were designed without using boolean algebra or synchronous clock and that "most literature on computers refers to these other methods of design" but he felt that as the circuits become more complex, boolean algebra and synchronous design will become needed methods in computer design. Great vision! \$\endgroup\$
    – PkP
    Jan 14, 2015 at 20:44
  • \$\begingroup\$ Any idea if that book is available on-line? It looks fascinating. The copyright may never lapse, but since I doubt the publisher expects to ever sell any more copies of it, it would seem like the sort of thing a publisher should be willing to have be freely available. \$\endgroup\$
    – supercat
    Jan 15, 2015 at 16:45
  • \$\begingroup\$ @supercat, indeed it's fascinating! And it's amazin how modern it is. Apart from the circuit physical implementation details and that it uses Veitsch diagrams instead of Karnaugh maps, It could be used in a university classroom today. The hardware it describes is ancient, but the design principles are sound and valid. I didn't find it available online, but it was in print for such a long time that it's quite easy to buy. Here's an Amazon link, is it allowed? (mods, please remove if it's not allowed) amazon.com/gp/product/0471688053 \$\endgroup\$
    – PkP
    Jan 15, 2015 at 17:13

The consensus seems to be that the "JK" is in honor of Jack Kilby, and the following is from:

ELECTRONIC INVENTIONS 1745-1976, By G.W.A. Drummer, ISBN 0-08-020982-3

enter image description here

  • \$\begingroup\$ Hi, and thanks for the interesting piece of history. I know that people often link up JK with Jack Kilby, but I'm interested in the original meaning of J and K - Jack Kilby wasn't even born when the flip flop was invented and he was quite young when the circuit was already called a JK flip-flop. So any accreditation to Jack Kilby would have been a later award. I would be quite interested to also know the origin of the whole "JK - Jack Kilby" story. Would you happen to know anything more about it? \$\endgroup\$
    – PkP
    Jan 14, 2015 at 19:26
  • \$\begingroup\$ Shouldn't this be an answer to [this question] rather than this? \$\endgroup\$
    – Nick T
    Jan 14, 2015 at 21:38
  • \$\begingroup\$ @NickT: to which question? \$\endgroup\$
    – SamB
    Jan 15, 2015 at 0:30
  • 2
    \$\begingroup\$ @SamB The linked question, electronics.stackexchange.com/questions/79884/… \$\endgroup\$ Jan 15, 2015 at 3:51

To my knowledge, the "D" for the D flip-flop stands for data. The reason for this, is that what ever "data" is on the input, it will be saved and "reflected" on the output, on the leading or falling edge of the clock. A typical application involves the use of 8 of them with their inputs connected to the data bus, when you pulse the clock, the data on the bus will be captured in the flip-flops and made available on their outputs. Although they can be used on different applications, this was their main application.


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