Memory Allocation

05/24/2009

These days I've been reading and thinking about memory allocation. As usual, I occasionally turned to Bill Buzbee Magic-1 computer for inspiration. I see that he has limited processes memory to 128K spited into two segments: 64KB code and 64KB data; the available linear address space gets distributed this way among different processes.

Actually, I'm seeking a different approach. I have established the premise that each process should believe it owns the entire 4GB linear space. Consequently, the CPU should interpret linear addresses provided by processes as nothing but off-sets within the designated physical memory space. My premise also implies that memory given to processes should not be limited.

This has been turned into kind of nightmare to me. I'm kind of lost between several decisions pending to be made: Whether to support variable-length structures from the CPU; whether to manage a Heap: a global heap or one per process... that kind of things.

Managing variable-length structures is complicated, so it contradicts my premise of keeping things simple at first though leaving room for further development. And yet there are many other things concerning Memory Allocation, such as fragmentation, cache and swaping.

My task for now is to figure out how a real program will run in my machine, and then decide who in the chain (CPU, OS, Compiler, Application code) will be taking care of which part.

05/25/2009

I worked this out and could get to some conclussions. See note "First Approach to Memory Allocation":