Control+Z is a control character in ASCII code. It is commonly used as a substitute (SUB) character. It is perhaps best known as the keyboard shortcut in Windows applications for the undo command. It is also used to signal an end-of-file on some operating systems. Strictly speaking, Control+Z is not a printable character but a code for control purposes, though it is sometimes rendered by two characters as ^Z. It is generated by pressing the Z key while holding down the Ctrl key on a computer keyboard. In many GUIs and applications Control+Z can be used to undo the latest action. In many applications earlier actions than the last one can also be undone by pressing Control+Z multiple times. Control+Z was one of a handful of keyboard sequences chosen by the program designers at PARC to control text editing. Presumably these particular keystrokes were chosen because of their location on a standard QWERTY keyboard, since the Z (undo), X (cut), C (copy), and V (paste) keys are located together at the left end of the bottom row of the standard QWERTY keyboard. In some operating systems, Control+Z is used to signal an end-of-file, and thus known as the EOF character (more accurately: the EOF control code), when typing at a terminal, terminal emulator, MS-DOS command line, or Win32 console. Early DEC operating systems used this convention, which was borrowed by CP/M, and was later in turn borrowed and continued in the MS-DOS and Microsoft Windows operating systems. On Unix-like systems, Control+Z is the most common default keyboard mapping for the key sequence that suspends a process (SIGTSTP). When entered by a user at their computer terminal, the currently running foreground process is sent a SIGTSTP signal, which generally causes the process to suspend its execution. The user can later continue the process execution by typing the command 'fg' (short for foreground) or by typing 'bg' (short for background) and furthermore typing the command 'disown' to separate the background process from the terminal. On Blogger, a weblog publishing service, the shortcut actually replaces the current version with the one last saved automatically.