OS Memory Management

Compaction is a process in which the free space is collected in a large memory chunk to make some space available for processes.

A dirty bit is a flag that indicates whether an attribute needs to be updated. Such situations usually occur when a bit in a memory cache or virtual memory page that has been changed by a processor but has not been updated in the storage.

A page is a fixed length memory block used as a transferring unit between physical memory and an external storage. A page fault occurs when a program accesses a page that has been mapped in address space, but has not been loaded in the physical memory.

RAM- Random Access Memory is a volatile form of memory. This means that the content written on RAM is wiped off when the power is turned OFF.

ROM – Read only memory like hard disks, tapes are ROM where the content once written is permanently written unless wiped off by the user..

The basic types of memories that a computer has are:

RAM Random access memory

ROM Read Only memory

Cache Memory

Other than these a computer also has secondary storage devices like a hard disk which also contribute towards it memory.

Single allocation is the simplest memory management technique. All the computer's memory, usually with the exception of a small portion reserved for the operating system, is available to the single application. MS-DOS is an example of a system which allocates memory in this way

Partitioned allocation divides primary memory into multiple memory partitions, usually contiguous areas of memory. Each partition might contain all the information for a specific job or task. Memory management consists of allocating a partition to a job when it starts and unallocating it when the job ends.

Paged allocation divides the computer's primary memory into fixed-size units called page frames, and the program's address space into pages of the same size. The hardware memory management unit maps pages to frames.

Segmented memory is the only memory management technique that does not provide the user's program with a 'linear and contiguous address space. Segments are areas of memory that usually correspond to a logical grouping of information such as a code procedure or a data array. Segments require hardware support in the form of a segment table which usually contains the physical address of the segment in memory, its size, and other data such as access protection bits and status