Memory Allocation Techniques in OS

Questions and Answers

What is the purpose of transferring low priority processes to a reserved memory area in secondary storage?

To reduce the number of context switches

To free up space in main memory for higher priority processes (correct)

To improve the performance of the short-term scheduler

To increase the priority of the process

What is the primary function of the long-term scheduler?

Selecting the next process to run from the ready queue

Context switching between processes

Handling interrupts generated by I/O devices

Deciding which processes to load into main memory (correct)

What occurs during context switching?

The process is terminated and removed from memory

The process is paused and resumed later

The process is swapped out to secondary storage

The CPU is deallocated from the currently running process and allocated to another process (correct)

What is the purpose of virtual memory?

To provide a reserved memory area for low priority processes Signup and view all the answers

Which type of scheduler is responsible for selecting the next process to run from the ready queue?

Short-term scheduler Signup and view all the answers

What is the result of swapping low priority processes to secondary storage?

Improved system performance Signup and view all the answers

What occurs when a higher priority process arrives in the queue?

The low priority process is swapped out to secondary storage Signup and view all the answers

What is the relationship between virtual memory and main memory?

Virtual memory is a separate memory area in secondary storage Signup and view all the answers

What is the primary goal of memory management in operating systems?

To effectively utilize the limited main memory resource Signup and view all the answers

What is the term used to describe the process of transferring processes between main memory and secondary storage?

Swapping Signup and view all the answers

Study Notes

Memory Allocation Techniques

There are three main memory allocation techniques used by an Operating System (OS): Contiguous, Linked, and Indexed.

Contiguous Memory Allocation

Allocates disk space for a file as a single, contiguous block of storage.
All sectors or clusters required to store a file are located together in a sequential manner on the disk.
Advantages include easy implementation in ROM (Read-Only Memory) type storage media.
Disadvantages include limitations in dynamic file size changes and inefficient use of disk space.

Linked Memory Allocation

Allocates disk space for files in a non-contiguous manner using a linked list data structure.
Each block of disk space contains a link (pointer) to the next block in the sequence, forming a chain of blocks that make up the file.
The directory entry contains the starting block's address.
Easy to extend file size by updating the last block in the sequence.

Indexed Memory Allocation

Allocates disk space for files in a non-contiguous manner using an index (allocation table or allocation map).
Each file is assigned a unique index block, which contains a list of pointers to the blocks of disk space allocated to the file.
The index block also contains metadata such as the file's size and attributes.

Fragmentation and Defragmentation

Fragmentation occurs when files are stored in non-contiguous blocks (fragments) on a storage device.
Fragmentation can occur naturally over time as files are created, modified, and deleted on the disk.
Defragmentation is the process of reorganizing the fragments into contiguous blocks to improve disk performance and efficiency.

Process Management

A program is a set of instructions that define a task.
A process is an instance of a program in execution, including current activity, memory, and system resources.

Virtual Memory

Virtual memory is a reserved memory area in secondary storage used to transfer low-priority processes from main memory.
Transferring between virtual memory and main memory is known as swapping.
Virtual memory allows for more efficient use of main memory.

Schedulers

There are three types of schedulers: Long-term, Mid-term, and Short-term.
Long-term schedulers decide which programs to load into memory.
Mid-term schedulers decide which suspended processes to load back into memory.
Short-term schedulers decide which process to execute next.

Context Switching

Context switching involves deallocating the CPU from the currently running process and allocating it to another process.
It involves switching the context (including the running state) of the CPU between processes.