ARCHIVED: What does the NumLock key do?

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The NumLock key changes the operation of the numeric keypad keys on a PC-style keyboard.

Pressing the NumLock key will toggle the status of NumLock and change the resulting behavior of the keypad keys:

When NumLock is active, usually indicated by a small light on the keyboard, the number keys on the keypad behave as numbers. Pressing a particular number has the same effect as pressing the number keys above the alphabetic section of the keyboard.
When NumLock is off, the keypad keys perform the functions shown below the numbers on their keycaps. The 4 key becomes a left arrow key, for example, and 3 becomes PgDn.

This feature lets you use the keypad not only for entering numbers in a spreadsheet, for example, but also for moving the cursor around in a word processor. Note that these functions are all duplicated by the arrow and document movement keys just to the left of the numeric keypad on a standard 101-, 102-, or 104-key keyboard; which keys you use is a matter of your own preference.