Memory management
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Memory management is the act of systematically managing computer memory. In its simplest forms, this involves providing ways to allocate portions of memory to programs at their request, and freeing it for reuse when no longer needed.
Virtual memory systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the effectively available amount of RAM using disk swapping. The quality of the virtual memory manager can have a big impact on overall system performance.
Garbage collection is the automated allocation, and deallocation of computer memory resources for a program. This is generally implemented at the programming language level and is in opposition to manual memory management, the explicit allocation and deallocation of computer memory resources.
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[edit] Goals
A number of different memory management techniques have been used, and improved upon, in operating systems. The principal goals of an operating system's memory management are:
- to provide memory space to enable several processes to be executed at the same time
- to provide a satisfactory level of performance for the system users
- to protect each program's resources
- to share (if desired) memory space between processes
- to make the addressing of memory space as transparent as possible for the programmer
[edit] Features
Memory management systems on multi-tasking operating systems usually deal with the following issues.
[edit] Relocation
In systems with virtual memory, programs in memory must be able to reside in different parts of the memory at different times. This is because when the program is swapped back into memory after being swapped out for a while it can not always be placed in the same location. Memory management in the operating system should therefore be able to relocate programs in memory and handle memory references in the code of the program so that they always point to the right location in memory.
[edit] Protection
Processes should not be able to reference the memory for another process without permission. This is called memory protection, and prevents malicious or malfunctioning code in one program from interfering with the operation of other running programs.
[edit] Sharing
Even though the memory for different processes is protected from each other different processes should be able to share information and therefore access the same part of memory.
[edit] Logical Organization
Programs are often organized in modules. Some of these modules could be shared between different programs, some are read only and some contain data that can be modified. The memory management is responsible for handling this logical organization that is different from the physical linear address space. One way to arrange this organization is segmentation.
[edit] Physical Organization
Memory is usually divided into fast primary storage and slow secondary storage. Memory management in the operating system handles moving information between these two levels of memory.
[edit] See Also
- Dynamic memory allocation
- Garbage collection
- Reference
- Page table
- Paging
- Demand paging
- Pointer
- Virtual memory
[edit] External Links
