Tarbell to Cromemco

In an alternate world DEC would have released the VT180 computer expansion with the VT100 in 1978, or soon afterward. The VT100 was a huge hit in and of itself; customers having the option to expand the terminal to a "real" CP/M computer, or buy the VT100+VT180 together, could have completely taken out Cromemco/Godbout/Morrow/IMSAI/Vector, and much of what drove demand for TRS-80. (Apple would have taken a hit, too, but would have survived thanks to VisiCalc.) DEC was a known quantity; these new startups weren't.

... But that would never have happened, because:

* DEC in 1978 would, as you said, not have been interested in personal computers.

* Further, DEC in 1978 would never have released a computer running a non-DEC operating system. Customers running Unix on PDP-11 was bad enough. It might have tried to squeeze the PDP-11 into a very compact form factor, as happened with the Heath H11, but that means running RT-11.

* Finally, much of what drove Cromemco/Godbout/Morrow/etc.'s sales was the VAR/SI market that quickly emerged because they, as startups, did not have existing field sales/service operations. I don't know how suited DEC's sales force would have been for selling to the small businesses that bought turnkey accounting/financial systems from VARs. Word processing was an existing market, but I think the customers that bought DEC WP-8 were larger than those that bought WordStar CP/M systems through VARs.

DEC wasn't alone in this. The only large technology company that released a CP/M computer before the IBM PC was Xerox, and the 820 came out just one month before the PC. Even Tandy went with the horrible TRSDOS when it could have also sewn up the CP/M market by going with the latter in 1977, instead of intentionally making the TRS-80 incompatible with CP/M out of the box.

40 years later, the list of things that IBM did right with the PC still amazes, especially considering how many things all of its rivals did wrong (and all the things IBM did wrong after Don Estridge's death in 1985).