In vim, why is 'j' used for down and 'k' for up?

Question

I've been using vim for many years and have never really thought about it. A friend of mine asked why that is, noting that in our culture, left would usually map to up while right would map to down, making the vim keys backwards. I understand that they are on the home row, meaning that you do not have to move your fingers anywhere to hit them, but that's a different point altogether. Basically, my question is: does anyone know why these keys were given their present purposes? It would be great if you could point me to some documentation on the decision as well.

Answer 1

The answer is in the wikipedia entry for vi. Bill joy, who wrote the visual mode of ex - which ended up being vim precursor vi - used a Lear Siegler ADM3A terminal on which the H, J, K, L keys mapped to left, down, up, right - and its been that way ever since.

Here's the keyboard layout:

A couple of other points of note on the ADM3A layout:

• Left of the Q: the escape key - somewhat handier than where it is on keyboards today, hence a good choice for switching between normal and insert modes.
• Top right: the 'Home' key doubles as the tilde (~), which subsequently became shorthand for a Unix user's home directory.