Comment by rep_lodsb

That's greatly oversimplified, or less generously, just flat out wrong. Win32 programs have always had their own isolated address space. That infamous BSOD is the result of memory protection hardware catching an access to something outside of that address space. When you open a DOS box, it uses the paging and V86 hardware mechanisms to create a new virtual machine, even though it shares some memory with the instance of DOS from which Windows was booted.

What Windows 9x didn't have was security. A program could interfere with these mechanisms, but usually only if it was designed to do that, not as a result of a random bug (if the entire machine crashed, it was usually because of a buggy driver).