In 1980 IBM sent reps to Gary Kildall, president of Digital Research, Inc (DRI), in his California office looking for an operating system for their PC. DRI had an operating system called CP/M. Talks with IBM were inconclusive and IBM went to Bill Gates. Mr. Gates had originally sent IBM to Mr. Kildall because he was too busy improving BASIC, but later accepted the assignment when they came back.

In 1984, DRI asked Stok Software to help develop Concurrent PC-DOS in hopes of re-capturing the Operating System market lost to Microsoft. Stok Software wrote the complete hard disk backup program (BackRest) used in Concurrent PC-DOS. Stok also worked on the Concurrent PC-DOS Program Manager routines.

As everyone knows, Microsoft's DOS and Windows became the industry chosen Operating Systems. DRI was ultimately purchased by Novell.