Vax's had modified bits, 68030s had both (dirty managed in software), 80x896s have both [an 'unnamed' risc architecture (I worked on) had both, managed in softw

Vax's had modified bits, 68030s had both (dirty managed in software), 80x896s have both [an 'unnamed' risc architecture (I worked on) had both, managed in software] The big advantage of handling this stuff in software is that any hardware doing this has to go through the system caches which is just really messy - better to use the existing coherent paths already provided and provide hardware support so you don't have to do this often