And let's not forget all the C applications that had been written for DEC VAX Unix systems that de-reference memory address zero to find their base address, where on the Sun machines with hard virtual memory doing this operation (now in system memory space) upset the kernel into quite a panic.

My first Sun Workstation was a Sun-1, running SunOS 0.3, in 1983. It was so new, there was no GUI window system, basically the display was a command-line ascii terminal on the workstation screen. Sun soon shipped SunOS 1.0 including SunWindows, their first bit-mapped GUI. I was at a university, and had full source code, so we had a fun time hacking the primitive window interface into something more interesting.