Discuss about the implementation of fixed size block and variable size block dynamic memory allocation.

Fixed Size Block Dynamic Memory Allocation

In fixed size block dynamic memory allocation, the memory is divided into blocks of equal size. When a memory request is made, the smallest block that can accommodate the request is allocated. The remaining space in the block is wasted.

The simplest implementation of fixed size block dynamic memory allocation is the Buddy System. In the Buddy System, the memory is divided into blocks of power of 2 sizes. When a memory request is made, the smallest block that can accommodate the request is allocated. If the block is larger than the request, it is split into two equal-sized blocks. The process continues until a block of the desired size is obtained. The unused blocks are kept in a free list.

When a memory block is freed, it is merged with its buddy block, if the buddy block is free. This process continues until a block of the largest size is obtained. The largest block is then added to the free list.

The Buddy System has the following advantages:

• It is simple to implement.
• It has low overhead.
• It guarantees that all memory requests can be satisfied, as long as there is enough memory available.

However, the Buddy System also has some disadvantages:

• It can lead to fragmentation, as the unused space in a block cannot be used by other requests.
• It can be difficult to find a block of the desired size, as the blocks are of power of 2 sizes.

Variable Size Block Dynamic Memory Allocation

In variable size block dynamic memory allocation, the memory is not divided into blocks of equal size. Instead, the memory is allocated in blocks of variable size. The size of a block is determined by the size of the memory request.

The simplest implementation of variable size block dynamic memory allocation is the First-Fit Algorithm. In the First-Fit Algorithm, the first block that is large enough to accommodate the memory request is allocated. If there is no block that is large enough, the request is denied.

The First-Fit Algorithm is simple to implement, but it can lead to fragmentation, as the unused space in a block cannot be used by other requests.

To reduce fragmentation, a number of other variable size block dynamic memory allocation algorithms have been developed. These algorithms include:

• Best-Fit Algorithm: The Best-Fit Algorithm allocates the block that is the closest in size to the memory request. This algorithm reduces fragmentation, but it can be more difficult to implement than the First-Fit Algorithm.
• Worst-Fit Algorithm: The Worst-Fit Algorithm allocates the largest block that is available. This algorithm also reduces fragmentation, but it can lead to more internal fragmentation, as the unused space in a block is larger.
• Next-Fit Algorithm: The Next-Fit Algorithm starts searching for a block from the last block that was allocated. This algorithm reduces fragmentation, but it can be more difficult to implement than the First-Fit Algorithm.

The choice of which variable size block dynamic memory allocation algorithm to use depends on the specific application.

Comparison of Fixed Size Block and Variable Size Block Dynamic Memory Allocation

Fixed size block dynamic memory allocation is simpler to implement and has lower overhead than variable size block dynamic memory allocation. However, fixed size block dynamic memory allocation can lead to fragmentation, as the unused space in a block cannot be used by other requests. Variable size block dynamic memory allocation can reduce fragmentation, but it can be more difficult to implement and can lead to more internal fragmentation.

The following table summarizes the key differences between fixed size block and variable size block dynamic memory allocation:

Feature	Fixed Size Block	Variable Size Block
Simplicity of implementation	Simple	More complex
Overhead	Low	Higher
Fragmentation	Can occur	Can be reduced
Internal fragmentation	No	Can occur

Conclusion

Fixed size block and variable size block dynamic memory allocation are two different approaches to managing memory. Fixed size block dynamic memory allocation is simpler to implement and has lower overhead, but it can lead to fragmentation. Variable size block dynamic memory allocation can reduce fragmentation, but it can be more difficult to implement and can lead to more internal fragmentation. The choice of which approach to use depends on the specific application.