How Does Contiguous Memory Allocation Work?

Here’s a step-by-step overview of how contiguous memory allocation works:

Also Read: Critical Section Problem in Operating System

Memory Initialization: The computSer’s memory is initialized and divided into various partitions or segments based on the memory allocation strategy being used.

Loading the Operating System: The operating system is loaded into memory when the system’s start up. The operating system kernel takes control and manages the execution of various processes.

Process Request: When a user initiates the execution of a program or a process, the operating system identifies the memory space required for that process.

Memory Allocation: The operating system searches for a contiguous block of memory that is large enough to accommodate the entire process. This block should be available in the main memory.

Memory Protection: The operating system sets up memory protection mechanisms to prevent one process from accessing the memory space of another. This ensures that each process operates in isolation.

Loading the Process: The process’s executable code, data, and stack are also loaded into the allocated contiguous memory space.

Process Execution: The CPU begins executing the process from its starting memory address. The process continues to execute until it completes or is interrupted.

Deallocation: When the process finishes execution or is terminated, the allocated memory is deallocated and marked as available for future use.

Types of the Contiguous Memory Allocation Approaches

There are two main approaches to implementing contiguous memory allocation: fixed-size partitioning and variable-size partitioning

Also Read: What is Virtual Memory in OS? Examples, Types, and Uses!

Fixed-Size Partitioning

In this approach, the memory is divided into fixed-sized partitions, and each process is assigned a contiguous block of memory based on its size. This technique is also known as static partitioning. The partitions may or may not be the same size. It can lead to internal fragmentation, restrict process size, and limit the degree of multiprogramming.

Advantages of Fixed-Size Partitioning:

Simplicity: Fixed-size partitioning is straightforward and easy to implement.

No External Fragmentation: Since, the memory is divided into fixed-sized partitions, there is no external fragmentation.

Predictability: The size of each partition is known in advance, making it easier to predict and manage memory usage.

Disadvantages of Fixed-Size Partitioning:

Internal Fragmentation: Each partition may not be fully utilized by a process, leading to internal fragmentation.

Inflexibility: Fixed-size partitions may not be suitable for varying sizes of processes, resulting in wasted memory for smaller processes or inability to accommodate larger processes.

Low Memory Utilization: The fixed sizes may not match the actual needs of the processes, leading to inefficient use of memory.

Limited Concurrent Processes: Only a specific number of processes can be accommodated based on the number of fixed partitions, limiting concurrent execution.

Variable-Size Partitioning

In this approach, the memory is divided into variable-sized partitions, and each process is assigned a contiguous block of memory based on its size. This technique allows for more efficient memory utilization, reduced external fragmentation, and a higher degree of multiprogramming. However, it is more complex to implement, involves more overhead, and still has the potential for external fragmentation.

Advantages of Variable-Size Partitioning:

Flexible Memory Allocation: Variable-size partitioning allows for more efficient use of memory by accommodating processes of varying sizes.

Reduced Internal Fragmentation: Since partitions can adjust dynamically to the size of the process, there is less internal fragmentation compared to fixed-size partitioning.

Better Memory Utilization: Variable-size partitions can lead to higher memory utilization as they can be tailored to the actual needs of the processes.

Accommodates Varying Workloads: Suitable for systems with varying workloads and diverse memory requirements.

Disadvantages of Variable-Size Partitioning:

External Fragmentation: Variable-size partitioning may suffer from external fragmentation, where free memory is scattered in small blocks throughout the system.

Complexity: Implementation can be more complex compared to fixed-size partitioning, requiring additional algorithms for dynamic partition management.

Overhead: There may be some overhead associated with managing variable-size partitions dynamically.

Difficulty in Predicting Memory Usage: The dynamic nature of variable-size partitioning makes it harder to predict and manage memory usage compared to fixed-size partitioning.

Strategies for Contiguous Memory Allocation Input Queues

There are several strategies for contiguous memory allocation, including first-fit, best-fit, and worst-fit. These strategies determine how memory is allocated to processes from the available free memory partitions.

First Fit Allocation

The first-fit allocation is a memory allocation technique used in operating systems to allocate memory to processes. It involves the operating system searching through the list of free blocks of memory, starting from the beginning of the list, until it finds a block that is large enough to accommodate the process.

Also Read: What is Semaphore in OS? Types with Examples & Their Operations

For Example:

Suppose you have the following free memory blocks in your system:

Block A: 200 KB

Block B: 100 KB

Block C: 300 KB

Block D: 150 KB

Now, let’s say a process arrives requesting 180 KB of memory. The system would allocate the memory from the first block that is large enough to accommodate it. In this case, it would be Block A (200 KB). After allocation, the memory blocks would look like this:

Block A: 20 KB (remaining)

Block B: 100 KB

Block C: 300 KB

Block D: 150 KB

Best Fit Allocation

In best fit allocation, operating system finds the smallest available memory block that can accommodate the process being allocated, i.e., the best-fit algorithm looks for the memory block closest in size to the requested process size. The algorithm aims to minimize memory wasting by allocating the smallest possible memory block to the process.

Here’s an example of the best-fit allocation:

Memory Blocks: Suppose we have the following available memory blocks: {100, 50, 30, 120, 35}.

Process Requirements: We have two processes, P1 with a size of 20 and P2 with a size of 60.

Allocation: In this example, the best-fit algorithm will allocate the memory block of size 30 to P1, as it is the smallest block that can accommodate P1’s size of 20. The memory allocation will look like this: {100, 30 (P1), 50, 35}.

Worst Fit Allocation

Worst Fit Allocation is a memory allocation strategy where the largest available block of memory is allocated to the incoming process. This strategy aims to maximize the utilization of memory by allocating the largest available block.

Here’s an example of the worst-fit allocation:

Memory Blocks: Suppose we have the following available memory blocks: {100, 50, 30, 120, and 35}.

Process Requirements: We have two processes, P1 with a size of 20 and P2 with a size of 60.

Allocation: In this example, the worst-fit algorithm will allocate the memory block of size 120 to P2, as it is the largest block available that can accommodate P2’s size of 60. The memory allocation will look like this: {100, 50, 30, 35 (P1), 120 (P2)}.

Other Strategies Are:

Next Fit Allocation

• Start the search for a suitable block from the location where the last allocation occurred.
• Reduces search time but may still result in fragmentation.

Buddy System

• Divide memory into fixed-size blocks and maintain a binary buddy system.
• When a process is allocated, find the smallest available block or split a larger block into two buddies.
• Helps reduce fragmentation and allows for efficient merging of adjacent free blocks.

Memory Compaction

• Periodically rearrange the allocated memory to consolidate free blocks and reduce fragmentation.
• Typically performed during periods of low system activity

Garbage Collection

• Automatically identify and reclaim memory occupied by processes that have completed or are no longer in use.
• Reduces fragmentation by freeing up memory that is no longer needed

Dynamic Partitioning

• Dynamically adjust the size of memory partitions based on the size of incoming processes.
• Helps optimize memory usage but requires efficient algorithms for dynamic resizing.

Memory Pooling

• Allocate memory from pre-allocated pools of fixed-size blocks.
• Can reduce fragmentation and improve memory utilization.

Page-Based Memory Allocation

• Divide memory into fixed-size pages, and allocate memory in page-sized chunks.
• Provides a balance between contiguous allocation and flexibility

Characteristics of Contiguous Memory Allocation

Here are the major characteristics of contiguous memory allocation:

Also Read: Deadlock Detection in OS with Algorithms and Examples

Contiguous Blocks: Memory is divided into contiguous blocks, and each process is allocated a single, contiguous block of memory for its execution.

Fixed-Size Partitions or Segments: The user process region is often divided into fixed-size partitions or segments, simplifying memory management.

Sequential Access: Contiguous memory allocation allows for sequential access to memory locations, making it suitable for applications that benefit from sequential data access.

Simple Implementation: Contiguous memory allocation is relatively simple to implement compared to more complex memory management schemes, making it suitable for resource-constrained systems.

Reduced Internal Fragmentation: Internal fragmentation is generally reduced because each process is assigned a contiguous block of memory, minimizing wasted space within each block.

Memory Protection: Implementing memory protection mechanisms is often simpler with contiguous memory allocation since each process has its own contiguous memory space.

Advantages of Contiguous Memory Allocation

The advantages of contiguous memory allocation include:

Efficiency: Contiguous memory allocation is an efficient technique for memory management. Once a process is allocated contiguous memory, it can access the entire memory block without any interruption.

Low Fragmentation: Since the memory is allocated in contiguous blocks, there is a lower risk of memory fragmentation. This can result in better memory utilization, as there is less memory wastage.

Fast Access: It allows users to access files randomly and provides excellent read performance to the user.

Disadvantages of Contiguous Memory Allocation

The disadvantages of contiguous memory allocation include:

Also Read: Deadlock Prevention in OS with Their Algorithms and Techniques

Limited Flexibility: Contiguous memory allocation is not very flexible as it requires memory to be allocated in contiguous blocks. This can make it challenging to allow file growth.

Fragmentation: Over time, the disk may become fragmented, which can reduce the available memory space and make it difficult to allocate new processes that require contiguous blocks of memory.

Slow Access: Access to memory can be slower than non-contiguous memory allocation, as memory can only be allocated in contiguous blocks that may require additional steps to access.

FAQs (Frequently Asked Questions)

How does Contiguous Memory Allocation handle variable-sized processes?

In systems using contiguous memory allocation, the OS must allocate a block of memory that is large enough to accommodate the largest process. This can result in internal fragmentation, where a portion of the allocated memory may remain unused.

Can Contiguous Memory Allocation lead to memory leaks?

Yes, if a process fails to release the allocated memory properly, it can lead to memory leaks. The contiguous nature of the allocation can make it easier to overlook unused memory.

How does Contiguous Memory Allocation differ from Non-Contiguous Memory Allocation?

Contiguous memory allocation allocates a single block of memory for a process, while non-contiguous allocation allows a process to be scattered in different non-adjacent memory locations.

Which operating systems use Contiguous Memory Allocation?

Contiguous Memory Allocation is used in various types of operating system, especially in simpler or embedded systems. Older versions of Windows and some real-time operating systems may employ contiguous memory allocation.

How can fragmentation be mitigated in Contiguous Memory Allocation?

Compaction is a technique used to mitigate fragmentation. This involves shifting processes in memory to consolidate free memory into one large block. However, compaction can be resource-intensive and may not be suitable for real-time systems.

Does Contiguous Memory Allocation affect system performance?

In general, contiguous memory allocation can be efficient in terms of access speed. However, if fragmentation becomes severe, it can lead to performance issues, and the system may need to spend more time searching for suitable memory blocks for processes

Summing Up

Through this Article, you have been fully educated about what is contiguous memory allocation in operating system; involving with their types and examples with ease. If this article is useful for you, then please share it along with your friends, family members or relatives over social media platforms like as Facebook, Instagram, Linked In, Twitter, and more.

Also Read: Disk Management in Operating System with Diagram

If you have any experience, tips, tricks, or query regarding this issue? You can drop a comment!

Happy Learning!!