Process isolation is a set of different hardware and software technologies[1] designed to protect each process from other processes on the operating system. It does so by preventing process A from writing to process B.
Process isolation can be implemented with virtual address space, where process A's address space is different from process B's address space – preventing A from writing onto B.
Security is easier to enforce by disallowing inter-process memory access, in contrast with less secure architectures such as DOS in which any process can write to any memory in any other process.[2]