1. Computer system hardware resource sharing method which enables at least two non-concurrent users to exercise functionally separate operational access to the computer system's hardware resources while maintaining substantially incorruptible operating system and program software integrity for each user, comprising steps of: sharing a common utilization of at least a computational portion, a random access memory portion, and an operator interface portion of the computer system's hardware resources between at least a first user and a second user; interlinking at least a first hard disk drive and a second hard disk drive with the computer system's hardware resources; maintaining the first user's operating system software and program files on the first hard disk drive; maintaining the second user's operating system software and program files on the second hard disk drive; configuring the computer system's hardware resources to enable a selectable one of at least a first system operating mode enabling the first user access to the first hard disk drive while denying functional access to the second hard disk drive, and a second system operating mode enabling the second user access to the second hard disk drive while denying functional access to the first hard disk drive; selecting between one of a first interval of operation including the first user and the first system operating mode, and a second interval of operation including the second user and the second system operating mode during an initial ROM-BIOS controlled POST sequence of the computer system and preferably prior to a BOOT of the operating system.