Contiguous Allocation - STORAGE MANAGEMENT

Contiguous Allocation

Each process is contained in a single contiguous section of memory.

· There are two methods namely :

· Fixed – Partition Method

· Variable – Partition Method

· Fixed – Partition Method :

o Divide memory into fixed size partitions, where each partition has exactly one process.

o The drawback is memory space unused within a partition is wasted.(eg.when process size < partition size)

· Variable-partition method:

o Divide memory into variable size partitions, depending upon the size of the incoming process.

o When a process terminates, the partition becomes available for another process.

o As processes complete

2.Segmentation

o Memory-management scheme that supports user view of memory

o A program is a collection of segments. A segment is a logical unit such as Main program, Procedure, Function, Method, Object, Local variables, global variables, Common block, Stack, Symbol table, arrays

3.Demand Paging

It is similar to a paging system with swapping.

o Demand Paging - Bring a page into memory only when it is needed

o To execute a process, swap that entire process into memory. Rather than swapping the entire process into memory, however, we use ―Lazy Swapper‖

o Lazy Swapper - Never swaps a page into memory unless that page will be needed.

o Advantages

· Less I/O needed

· Less memory needed

· Faster response

· More users

4.Page Replacement Algorithms

1. FIFO Page Replacement

2. Optimal Page Replacement

3. LRU Page Replacement

4. LRU Approximation Page Replacement

5. Counting-Based Page Replacement