Arrow Keys History
First Keyboard with Embedded Arrow Keys
Who invented the arrow keys?
The first keyboard to have embedded arrow keys is probably SAIL Keyboard. 1970. Although not dedicated arrow keys. It has arrows ← → ↔ ↑ ↓ embedded on J K L ; :
← → ↔ ↑ ↓ j k l ; :

The ADM-3A Terminal year 1976 is probably also a big influence.
First keyboard with dedicated arrow keys
The first to have dedicated arrows is maybe Space Cadet Keyboard (year ~1980) It has thumb keys 👍 👎 👈 👉 But these keys are not documented in manual. Not used by default.

Arrow Keys Arrangement
Inverted T
first inverted T arrangement is probably DEC LK201 keyboard, 1983.

left down up right
First is probably ADM-3A terminal, 1976

up down left right

left right down up

Cross

Diamond





Horizontal Diamond
Arrows Square


Split Arrows
Efficiency of Arrow Keys Arrangement
Arrow Keys Arrangement Efficiency: vim HJKL vs IJKL
[history of the inverted T arrow key arrangement on keyboard By Jim Burrows. At http://www.eldacur.com/~brons/NerdCorner/InverseT-History.html ]
2018-07 thanks to Marcin Wichary
2018-07-12 to read [The Keys To Success. A lot of early video game consoles secretly wanted to be home computers, too: Their makers either sold keyboard add-ons or failed miserably in the process. By Ernie Smith. At https://tedium.co/2017/04/27/video-games-keyboards-intellivision/ ]