[1] On IBM PC compatible personal computers from the 1980s, the BIOS allowed the user to hold down the Alt key and type a decimal number on the keypad.
Some Eastern European, Arabic and Asian computers used other hardware code pages, and MS-DOS was able to switch between them at runtime with commands like KEYB, CHCP or MODE.
][clarification needed] This input method is emulated by many pieces of software (such as later versions of MS-DOS and Windows) that do not use the BIOS keyboard decoding.
To enable it, a user must set or create a string type (REG_SZ) value called EnableHexNumpad in the registry key HKEY_CURRENT_USER\Control Panel\Input Method, assign the value data 1 to it, and then reboot or log out/in.
However, numeric entry of Unicode characters is possible in most Unix or Unix-like OSs by pressing and releasing Ctrl+⇧ Shift+U, and typing the hex number followed by the space bar or enter key.
For example, If Num lock is disabled, attempting an Alt code may cause unexpected results in some applications, due to the controls used on the same key.