In D flip flop, D means DATA. In SR flip flop, S means SET and R means RESET. What is the meaning of JK flip flop's J and K?

  • \$\begingroup\$ Only speculation, but quaternions use i, j, and k as unit vectors, such that i*j*k = -1. The flip-flop might be adopting this convention. Then it would be computing Q*J*K with Q=±1, J=1 or j, K=1 or k, the next state being Q=1 if the result is 1, k, or -k, else Q'=1 if -1, j, or -j. (Perhaps another formulation is more elegant.) \$\endgroup\$ Commented Jan 16, 2015 at 1:56
  • \$\begingroup\$ can we unprotect this so it can be closed as primarily opinion based? \$\endgroup\$
    – old_timer
    Commented Oct 13, 2019 at 14:42
  • \$\begingroup\$ A recent answer to a very similar question provided evidence that the correct answer is not opinion-based. \$\endgroup\$ Commented Oct 14, 2019 at 18:06
  • \$\begingroup\$ As pointed out in this post, the D in the D flip-flop was originally intended to stand for "delay." (Phister, 1958) \$\endgroup\$
    – JRN
    Commented Apr 9, 2020 at 8:03

1 Answer 1


Here's what wikipedia says: -

According to P. L. Lindley, a JPL engineer, the flip-flop types discussed below (RS, D, T, JK) were first discussed in a 1954 UCLA course on computer design by Montgomery Phister, and then appeared in his book Logical Design of Digital Computers. Lindley was at the time working at Hughes Aircraft under Dr. Eldred Nelson, who had coined the term JK for a flip-flop which changed states when both inputs were on. The other names were coined by Phister. They differ slightly from some of the definitions given below. Lindley explains that he heard the story of the JK flip-flop from Dr. Eldred Nelson, who is responsible for coining the term while working at Hughes Aircraft. Flip-flops in use at Hughes at the time were all of the type that came to be known as J-K. In designing a logical system, Dr. Nelson assigned letters to flip-flop inputs as follows: #1: A & B, #2: C & D, #3: E & F, #4: G & H, #5: J & K. Nelson used the notations "j-input" and "k-input" in a patent application filed in 1953.

Here is a link to a Jack Kilby biography that says he started at TI in 1958 and doesn't mention JK flip flops at all.

This TI website about Jack Kilby also doesn't mention JK flip flops either

If you look halfway down column 13 of this patent filed in 1953 (Granted 1958) you will see mention of inputs to a flip flop called J and K. This patent pre-dates Jack Kilby's time at TI by 5 years: -

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  • 2
    \$\begingroup\$ And of course the letter I was probably skipped for the same reason that we use \$j = \sqrt{-1}\$ in electronics. :) \$\endgroup\$
    – Kaz
    Commented Aug 24, 2013 at 0:07
  • \$\begingroup\$ @Kaz - don't mention that to the mathematics guys \$\endgroup\$
    – Andy aka
    Commented Aug 24, 2013 at 0:09
  • 1
    \$\begingroup\$ @Kaz: I don't think so: as much as I know often the letter i is skipped when letters are used for numbering (actually "lettering") because i and j or I and 1 look so similar and may get confused. It is rather an optional convention. In electronics it seems to be another problem (often it's no problem when several very similar letters are used at the same time: e.g. \$\nu\$ and v or \$\omega\$ and w etc.). The problem in electronics is that exactly the same letter i normally used for imaginary unit is also used for current. So one must yield necessarily. \$\endgroup\$
    – Curd
    Commented Oct 24, 2016 at 21:58
  • \$\begingroup\$ So it's been long since I was in school, but as soon as I read the question, my memory told me: "Jordan & Kelly". So I've tried searching for it, and wikipedia tells me: "The first electronic flip-flop was invented in 1918 by [...] William Eccles and F. W. Jordan." So the 'Jordan' could be right (tribute to him?). Maybe my 'Kelly' should be 'Kilby' but that's not what I recall, and it's pretty clear by now that he had nothing to do with it. Anyone ever heard of this 'Jordan & Kelly(?)' explanation? Or is my memory failing me? \$\endgroup\$
    – MartinF
    Commented Aug 15, 2018 at 12:23

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