memory protection is what changed. there are different ways to set it up and others here will be much more knowledgeable, but the OS works in conjunction with CPU features to generate an error if a program attempts to access memory not allocated to it.
before (I think) the 386, microprocessors didn't support proper memory protection, any OS that attempted to run multiple programs was at risk that one program would crash the system. You might see the 'bomb' dialog on Mac or it might just freeze. Blue screen I think started with Windows 95. Until (I think) Windows NT and Mac OSX the OS didn't implement memory protection. Original Mac had cooperative multitasking, each program was supposed to run in a loop that yielded to the OS so it could e.g. move the mouse pointer, process clicks. Of course at that time DOS didn't have any multitasking. although there was the infamous "TSR" terminate and stay resident feature which was used by e.g. DesqView to allow you to switch programs via a hotkey.
before (I think) the 386, microprocessors didn't support proper memory protection, any OS that attempted to run multiple programs was at risk that one program would crash the system. You might see the 'bomb' dialog on Mac or it might just freeze. Blue screen I think started with Windows 95. Until (I think) Windows NT and Mac OSX the OS didn't implement memory protection. Original Mac had cooperative multitasking, each program was supposed to run in a loop that yielded to the OS so it could e.g. move the mouse pointer, process clicks. Of course at that time DOS didn't have any multitasking. although there was the infamous "TSR" terminate and stay resident feature which was used by e.g. DesqView to allow you to switch programs via a hotkey.
typically software can't fry hardware, even the famous 'halt and catch fire' instruction didn't literally cause a fire https://en.wikipedia.org/wiki/Halt_and_Catch_Fire_(computing...