If you are a Gmail user, with keyboard short codes enabled then you might have noticed that you can use j and k keys for navigation within GMail. You can use J key to navigate to previous (older) message & K key to navigate to the newer message from your inbox. Even the navigation using J and K keys is quite popular in others website also such as makeuseof.com , Google Reader and even at tumblr also. This J-K key combination may be found at many blog sites also. Even many developers use this keys in their applications for navigation purposes.
Now the question is why J & K only. Why not others ?
The history is quite interesting. Let’s have a look on it.
Everything is started from UNIX era. When Bill Joy created the vi text editor for Unix, he used a ADM-3A terminal. The fact of this terminal is, the keyboard didn’t have the arrow keys. You can see the layout of ADM-3A terminal’s keyboard in above illustration. Instead the keys h, j, k and l were inscribed with arrow symbols and these keys, in combination with the Ctrl key, were used for moving the cursor on the screen.
Now time is changed. Now-a-days the keyboard got dedicated arrow keys. Layout is changed. But still same J & K keys are still popular for navigation. UNIX is a most known operating system and have lot’s of developer worldwide & still they use J & K keys for navigation in their applications.