Memory Management in OS

Operating systems require memory management to function properly. It deals with how the computer system’s main memory is used. Its function is to transfer processes between secondary memory (R.O.M) and primary memory (R.A.M). Nowadays, the majority of operating systems use memory management. It improves the operating system’s effectiveness and performance.

What is Memory Management in Operating System?

Random access memory (primary memory) capability is controlled and managed by the OS using this mechanism. It is employed to improve memory utilization, system performance, and concurrency.
Processes are moved back and forth between primary and secondary memory by memory management. Additionally, it monitors the amount of free, allocated, and used memory.

Why use Memory Management in Operating system?

  • Every memory location’s status, including whether it is allocated or free, is monitored by memory management.
  • Computer systems can run programs that demand more main memory than is currently available on the system by using memory management. Data movement between primary and secondary memory is used to achieve this.
  • Memory management in OS takes care of the system’s main memory by offering abstractions that make the programs that are executing on the system assume they have been given a lot of memory.
  • Memory management’s responsibility is to prevent other processes from tampering with the memory that is allotted to all of the processes. If you don’t do this, the computer can behave strangely or improperly.
  • Memory management in OS enables processes to share memory spaces, allowing many programs to share the same memory address (although only one at a time).

What is Paging?

A computer system may access and use memory that is larger than the memory that is built into the computer hardware. Virtual memory is the term used to describe this additional memory. The computer system employs virtual memory, which is a component of secondary memory, as its main memory. In order to implement virtual memory, paging is crucial.

Every process’s code makes use of a collection of logical addresses known as the process address space. Blocking the process address space is a memory management method called paging. The units are called "pages," and each block has the same size. A page’s size is a power of 2, and its value falls between 512 and 8192 bytes. The quantity of pages in a process is used to determine its size.

A similar division of the main memory is done into blocks of fixed size. These blocks are known as “frames” and the size of a frame is the same as that of a page to achieve optimum usage of the primary memory and for avoiding external fragmentation.

Advantages of Paging:

  • Paging reduces external fragmentation.
  • Implementing paging is simple.
  • Paging improves memory performance.
  • Swapping becomes quite easy because the dimensions of the frames and pages are the same.
  • Paging is helpful for quick data access.

What is Fragmentation?

The available free space in primary memory is divided into smaller chunks when processes are relocated to and from the main memory. This occurs when a process’s memory requirements are greater than the size of the available memory, preventing memory from being allocated to the process. Such memory chunks are never used. This problem is known as Fragmentation.

Fragmentation is of the following two types:

1. External Fragmentation:
Although there is enough free main space to accommodate all processes, it cannot be used since it is not continuous. By combining or rearranging data in memory’s free memory blocks to create a single, bigger free memory block, external fragmentation can be reduced.
2. Internal Fragmentation:
When a process is given a memory block that is bigger than what the process actually needs, internal fragmentation occurs. A portion of memory is left unused in this case since no other process will use it. By giving a process access to the lowest free memory chunk that may be allocated, internal fragmentation can be reduced.

Operating System Memory Management Techniques

Following are the three major memory management techniques used in operating systems:
1. Segmentation
A technique for breaking up the main memory into many chunks called segmentation. Every block is referred to as a segment and has a certain length. Every segment has a base address that serves as its beginning point. The quantity of free memory that is present in a segment depends on its length.

The distance between a data item’s real position and the segment base address can be used to pinpoint where any data items stored in a segment are located. An offset or displacement value is used to describe this distance. Simply said, when data has to be retrieved from a segment, the actual address of the data is determined by adding the segment’s base address and offset value.
The offset value and the base address of a segment are both specified in a program instruction itself.

2. Paging
A computer system may access and use memory that is larger than the memory that is built into the computer hardware. Virtual memory is the term used to describe this additional memory. The computer system employs virtual memory, which is a component of secondary memory, as its main memory. In order to implement virtual memory, paging is crucial.

3. Swapping
An operating system uses the method of swapping to manage the computer system’s memory effectively. The two jobs of switching are swapping in and swapping out. Data blocks or pages are moved from the secondary memory to the primary memory by "swapping in." Blocks or pages of data are transferred from the main memory to the read-only memory (R.O.M.) during swapping. Swapping is helpful when running a large application or carrying out an operation on a huge file.

Conclusion

  • A strategy for controlling the operation of primary memory is known as memory management in Operating System. It is used to improve concurrency, system performance, and memory consumption.
  • Every memory location’s state, including whether it is allocated or free, is monitored by memory management.
  • Blocking the process address space is a memory management method called paging. The units are called "pages," and each block has the same size.
  • There are two types of fragmentation: internal and external.
  • The process of segmenting the main memory involves breaking it up into several pieces. Every block is referred to as a segment and has a certain length.
  • The two jobs of switching are swapping in and swapping out.

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