Hi guys,
sorry I didn`t read the whole thread...but here some notes from me. I suppose MP in this context means Multiprocessing, right?
It`s true that most comercial and free operating systems out there use a separate address space for each process. This is a design decision** and not mandatory nor necessary for a MP capable OS. It`s possible to have MP working on a single address space and to use the MMU to extend this space beyond the physical memory by using the page swaping techique and to handle memory protection. Shared resources must still be protected through mutexes or semaphores from concurrent CPU accesses. In a single (flat) address space OS (SASOS) message passing is done by passing pointers to the data in memory, just like AmigaOS does, there is no need to move or copy data around. Note that even in non-SASOS data is generally not copied around, it`s mapped with the help of the MMU, so both processes may see the same data in the same place or in case a process already allocated that virtual memory region for other stuff, in different memory places.
** in the early days of computing when there was 16 bit address spaces only, address translations didn`t make much sense because one could not get over the 16 bit address space with it. Earlier MMUs just swapped memory regions with the bank switching method, thus having many code blocks using the same adresses but only one at a time. In the 32 bit era this technique became obsolete and segmenting and paging took over. However, using for each process different address spaces mapped to the same region simplified program loading as programs could be linked statically and did not need to be relocated in memory. In the 64 bit era there is realy no need to have many address spaces any more. Newer research OSes (e.g. singularity from Microsoft) are in fact SASOS.
Best regards,
Leo24
