A hard disk (also called a "hard drive") is much like a filing cabinet. The programs and data are stored on the hard disk and the computer accesses them as needed. When the computer accesses the hard drive, it is reading the stored information into memory. That memory is the temporary workspace. The original file on the hard disk is left undisturbed. When the computer stores information, it writes the data to the hard disk. That process results in the old file being replaced or modified with the new information. If you save data to a new file, or install new software, the information is written to the disk in an available, unused portion of the disk.