Memory Allocation
Main memory usually has two partitions
- Low Memory -- Operating system resides in this memory.
- High Memory -- User processes then held in high memory.
Operating system uses the following memory allocation mechanism.
| S.N. | Memory Allocation | Description |
|---|---|---|
| 1 | Single-partition allocation | In this type of allocation, relocation-register scheme is used to protect user processes from each other, and from changing operating-system code and data. Relocation register contains value of smallest physical address whereas limit register contains range of logical addresses. Each logical address must be less than the limit register. |
| 2 | Multiple-partition allocation | In this type of allocation, main memory is divided into a number of fixed-sized partitions where each partition should contain only one process. When a partition is free, a process is selected from the input queue and is loaded into the free partition. When the process terminates, the partition becomes available for another process. |