Clayton Christensen's (1997) book The Innovator's Dilemma documents many cases of prominent firms failing to adapt to disruptive technological innovations. The history of the computer industry is largely a story of companies who fail to make such a shift to new technology. Of the original mainframe computer manufacturers, GE, RCA, Control Data, and Honeywell exited the business while Burroughs and Sperry Univac merged into Unisys (a relatively weak player) and NCR went through a tumultuous acquisition and later divestiture by AT&T. In the minicomputer market, the leaders were Digital Equipment Corp. (DEC), Data General, Prime, Hewlett-Packard, and Texas Instruments, of which only HP remains as an independent force in the industry. The original pioneers in personal computers were Apple, Tandy Corp., Atari, Commodore, and Texas Instruments with Apple being the only remaining manufacturer (with a market share under 5%).