DEC's demise was a combination of factors. They had successfully infiltrated research and education markets, but UNIX was a growing phenomenon and while it was short-term shrewd for DEC to allow VAXen to run UNIX instead of VMS, it invited price comparisons with other vendor's boxen. Business markets were too entrenched with IBM to change. Breaking into the PC market was another problem. Hardware standards hadn't hardened yet and DEC thought it there was some room for improvement. 1982's Rainbow sported both an 8088 for booting DOS and a Z80 for booting CP/M (and a third choice, an obscure 16-bit CP/M variant named CP/M-86), but unfortunately it also featured a proprietary floppy disk format, and many video incompatibilities. I remember seeing one of these when they came out at my high school and being distinctly unimpressed. Like many others, DEC realized compatibility was nonoptional, and they managed to survive almost another 2 decades making clones before they got priced out of the market.