Abstract: A computer sharing system which adapts a computer's hardware resources to providing virtual dual system operation for several non-concurrent system users. A separate hard disk drive including a full complement of boot, operating system, program and data file software is provided for each of the non-concurrent system users. Access by one system user to another system user's hard disk drive and attendant files is absolutely denied thereby preventing corruption of one user's hard disk dive files by another user's carelessness or malicious intent, or through unique setup adaptation of one user's program files which may otherwise interact with and impose unwanted changes on another's program file's operational performance. Each of the separate hard disk drives may be uniquely formatted to service totally different operating systems, including boot track code, in support of various operating systems including MS-DOS, Windows-NT, OS/2, Unix and others.