Memory Management

•  Memory consists of a large array of words or bytes, each with its own address. The CPU fetches instructions from memory according to the value of the program counter. These instructions may cause additional loading from and storing to specific memory addresses.
• Memory unit sees only a stream of memory addresses. It does not know how they are generated.
•  Program must be brought into memory and placed within a process for it to be run.
•  Input queue – collection of processes on the disk that are waiting to be brought into memory for execution.
• User programs go through several steps before being run.

Address binding of instructions and data to memory addresses can happen at three different stages.

• Compile time: If memory location known a priori, absolute code can be generated; must recompile code if starting location changes.
  Example: .COM-format programs in MS-DOS.
•  Load time: Must generate relocatable code if memory location is not known at compile time
• Execution time: Binding delayed until run time if the process can be moved during its execution from one memory segment to another. Need hardware support for address maps (e.g., relocation registers).