What do you mean by Paging?
- OS performs an operation for storing and retrieving data from secondary storage devices for use in main memory.
- Paging is a memory management technique in which the memory is divided into fixed size pages.
- Paging is used for faster access to data.
- When a program needs a page, it is available in the main memory as the OS copies a certain number of pages from your storage device to main memory.
- Data is retrieved from storage media by OS, in the same sized blocks called as pages.
- Paging allows the physical address space of the process to be non contiguous.
- The whole program had to fit into storage contiguously.
- Paging is to deal with external fragmentation problem.
- This is to allow the logical address space of a process to be non contiguous, which makes the process to be allocated physical memory.
- Flexibility- with a fully-developed paging approach, the system will be able to support the abstraction of an address space effectively, regardless of how a process uses the address space; we won’t, for example, make assumptions about the direction the heap and stack grow and how they are used.
- Simplicity- simplicity of free-space management that paging affords. For example, when the OS wishes to place our tiny 64-byte address space into our eight-page physical memory, it simply finds four free pages; perhaps the OS keeps a free list of all free pages for this, and just grabs the first four free pages off of this list.
- Memory protection ( malicious tasks can't harm each other or the kernel)
- Shared memory between tasks (a fast type of IPC, also conserves memory when used for DLLs)
- Demand loading (prevents big load on CPU when a task first starts running, conserves memory)
- Memory mapped files
- Virtual memory swapping (lets system degrade gracefully when memory required exceeds RAM size)
- paging eliminates fragmentation
- Support higher degree of multi programming
- Paging increases memory and processor utilization
- Compaction overhead required or the relocatable partition scheme is also eliminated
Disadvantages Of Paging
- Page address mapping hardware usually increases the cost of the computer.
- Memory must be used to store the various tables like page table,memory map table..
- Some memory will still be unused if te number of available block is not sufficient for the address spaces of the jobs to be run.
No comments:
Post a Comment