The "sticky bit", formally known as the "save text on swap" bit, derives its name from its original purpose. Originally the "sticky bit" caused a process's initial memory image to be stored as a contiguous image on the disk drive which was used to store real memory pages when they were not in use. This improved the performance of commonly executed commands by making the initial memory image readily available. Modern UNIX systems no longer perform that function when the bit is set, but the name has been preserved nonetheless. In the case of files, the "sticky-bit" may be used by the system to indicate the style of file locking to be performed. In the case of directories, the "sticky bit" prevents any process, other than one which has super-user privileges or one having an effective user ID of the file owner, from deleting a file within that directory. The "sticky bit" is most commonly used on publicly writable directories, such as the various temporary working space directories on the system.