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Memory Resource Management

 

Operating systems also manage the computer’s memory, typically dividing it into various parts for storing actual computer instructions (code), data variables, and the heap. The heap is a section of memory from which processes can allocate and free memory dynamically. Some operating systems provide a means for processes to address more memory than is physically present as RAM, a concept called virtual memory. With virtual memory, the computer’s memory can be expanded to include secondary storage, such as a disk drive, in a way that’s transparent to the processes. Operating systems create virtual memory using a hardware feature, available on some processors, called a memory map unit (MMU). MMU automatically remaps memory address requests to either physical memory (RAM) or secondary storage (disk) depending on where the contents actually reside. The MMU also allows some address ranges to be protected (marked read-only) or to be left totally unmapped. Virtual memory also has another benefit: In operating systems that support it, an MMU can be programmed to create a separate address space for each process. Each process can have a memory space all to itself and can be prevented from accessing memory in the address space of other processes.