Question

 Present an overview of the major approaches (methodologies) commonly used in memory allocation.

Answer 1

Memory allocation methodologies-There are two ways to allocate memory.These are
1) Contiguous memory allocation

2) Non Contiguous memory allocation

1) Contiguous memory allocation-In Contiguous memory allocation technique main memory is partitioned into two parts i.e.lower part (addresses) for operating system and higher addresses for user's program.But contiguous memory allocation technique leads to internal fragmentation.Contiguous memory allocation technique uses two approaches.
a) Fixed size or static Partition- Memory is divided into fixed size blocks.In fixed size partition drawback is that when
process size is equal to or greater than the block of memory then it can not be loaded it memory .But it supports multiprogramming .
b) variable size or dynamic Partition- In this approach memory is divided into variable size partition. When any process requests for memory it allocates exactly same amount of memory as required by process.After termination of the process the free memory can be allocated to another process. Dynamic partition uses following approach for allocation of memory.
i) Best Fit
ii) First Fit
iii) Worst Fit
iv) Last Fit

2) Non Contiguous memory allocation- In Non contiguous memory allocation technique operating system divides processes and allocates them at noncontiguous memory locations.In this approach wastage of memory can be reduced but it increases address translation.There are two ways for Non Contiguous memory allocation
a)Paging- In paging technique process address space i.e. logical address is divided into blocks of equal size.The equal
size blocks are known as Pages.It leads to internal fragmentation.
b)Segmentation- In segmentation technique process is partitioned into several segments of variable size.It leads to
external fragmentation.