Single partition allocation, Multiple-partition allocation and Fixed Equal-size partitions in operating system-computer world

 Single partition allocation, Multiple-partition allocation and Fixed Equal-size partitions in operating system

Single partition allocation

In this scheme operating system is residing in law memory and user process are executing in higher memory.

Advantages

1. It is simple 
2. It is easy to understand and use

Disadvantages

1. User job is limited to the size of available memory.
2. It leads to poor Utilization of processor and memory.

Multiple-partition allocation 

It is the simplest method for allocating  memory is divided memory into several fixed size partitions.

Fixed Equal-size partitions

It divides the main memory Into equal number of fixed sized partitions, operating system occupies some fixed portion and remaining portion of main memory is available for user processes.

Advantages

1. It supports multi programming.
2. A process whose size is less then or equal to the partitions size can be loaded into any available partition.

Disadvantages

1. If a program is big to fit into a partition use overlay technique.
2. Memory use is efficient.
3. Fixed variable size partitions
4. By using fixed variable size petitions we can overcome the disadvantage present in fixed equal size petitioning. With unequal-size partitions, there are two ways to assign processes to partitions.

Use multiple queues

One queue is present in each and every process. When a new process is to arrive it will put in the queue it is able to fit without wasting the memory space, irrespective of other blocks queues.

Use single queue

In this method only one ready queue is present for scheduling the jobs for all the blocks irrespective of size.