Memory Management

Memory Management

Memory management is the functionality of an operating system which handles or manages primary memory and moves processes back and forth between main memory and disk during execution.

It checks how much memory is to be allocated to processes. It decides which process will get memory at what time.

Process Address Space

The process address space is the set of logical addresses that a process references in its code.

The set of all logical addresses generated by a program is referred to as a logical address space. The set of all physical addresses corresponding to these logical addresses is referred to as a physical address space.

The runtime mapping from virtual to physical address is done by the memory management unit (MMU) which is a hardware device.

Static vs Dynamic Loading

Static loading, the absolute program (and data) is loaded into memory in order for execution to start.

Dynamic loading, dynamic routines of the library are stored on a disk in relocatable form and are loaded into memory only when they are needed by the program.

Fragmentation

As processes are loaded and removed from memory, the free memory space is broken into little pieces. It happens after sometimes that processes cannot be allocated to memory blocks considering their small size and memory blocks remains unused. This problem is known as Fragmentation.

Paging

Paging is a memory management technique in which process address space is broken into blocks of the same size called pages.

Main memory is divided into small fixed-sized blocks of (physical) memory called frames
And the size of a frame is kept the same as that of a page to have optimum utilization of the main memory and to avoid external fragmentation.

Address Translation
Page address is called logical address and represented by page number and the offset.
Logical Address = Page number + page offset

Frame address is called physical address and represented by a frame number and the offset.
Physical Address = Frame number + page offset

Reference

https://www.tutorialspoint.com/operating_system/os_memory_management.htm