Just to be clear, num lock is not the least popular item on a Chinese menu, nor is it a security measure for wayward nums. Actually, it is a key found on most computer keyboards near the 10-key numeric pad. The term is short for numeric lock or number lock, the function of which is now considered largely ornamental and historical. There is also a corresponding light which indicates when the key has been activated or deactivated.
When IBM first introduced personal computers, the original keyboards combined the standard 10-key numeric pads with a second set of cursor controls. The num lock key acted as a toggle switch between the two sets of commands. When the key was switched on, the numeric keypad would work exclusively as a form of calculator. Switching it off would convert the keys to cursor controls, allowing users to manipulate the cursor in four directions or send it to the top or bottom of the page.
More modern computer keyboards use separate keys for cursor control, reducing the need for a num lock key. The numerical keypad on almost all modern keyboards is set to lock by default. Occasionally, a computer will remember the setting during shut-down and restore that setting during restart. This means if the user turns off the num lock for gaming or programming purposes, it will remain off during the restart process.
The key has not become completely obsolete — there are still a few programming functions which benefit from its presence. Some computer gamers find that the numeric keypad is easier to manipulate than the separate direction and cursor control keys of modern keyboards. Web surfers may also find the unlocked numeric keypad to be useful while scrolling through large websites. The next generation of keyboard design may eliminate the num lock key altogether, but there was a time when it served a definite purpose for early computer users.