December 13, 2019
Amitraj
Memory Allocation
-> Memory allocation is a process by which computer programs are assigned memory or space. It is of three types :
First Fit:
The first hole that is big enough is allocated to program.
Best Fit:
The smallest hole that is big enough is allocated to program.
Worst Fit:
The largest hole that is big enough is allocated to program.
Fragmentation
Fragmentation occurs in a dynamic memory allocation system when most of the free blocks are too small to satisfy any request. It is generally termed as inability to use the available memory.
In such situation processes are loaded and removed from the memory. As a result of this, free holes exists to satisfy a request but is non contiguous i.e. the memory is fragmented into large no. Of small holes. This phenomenon is known as External Fragmentation.
Also, at times the physical memory is broken into fixed size blocks and memory is allocated in unit of block sizes. The memory allocated to a space may be slightly larger than the requested memory. The difference between allocated and required memory is known as Internal fragmentation i.e. the memory that is internal to a partition but is of no use.
Paging
A solution to fragmentation problem is Paging. Paging is a memory management mechanism that allows the physical address space of a process to be non-contagious. Here physical memory is divided into blocks of equal size called Pages. The pages belonging to a certain process are loaded into available memory frames.
Page Table
A Page Table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual address and physical addresses.
Virtual address is also known as Logical address and is generated by the CPU. While Physical address is the address that actually exists on memory.
Segmentation
Segmentation is another memory management scheme that supports the user-view of memory. Segmentation allows breaking of the virtual address space of a single process into segments that may be placed in non-contiguous areas of physical memory.
Segmentation with Paging
Both paging and segmentation have their advantages and disadvantages, it is better to combine these two schemes to improve on each. The combined scheme is known as 'Page the Elements'. Each segment in this scheme is divided into pages and each segment is maintained in a page table. So the logical address is divided into following 3 parts :
1. Segment numbers(S)
2. Page number (P)
3. The displacement or offset number (D)
-> Memory allocation is a process by which computer programs are assigned memory or space. It is of three types :
First Fit:
The first hole that is big enough is allocated to program.
Best Fit:
The smallest hole that is big enough is allocated to program.
Worst Fit:
The largest hole that is big enough is allocated to program.
Fragmentation
Fragmentation occurs in a dynamic memory allocation system when most of the free blocks are too small to satisfy any request. It is generally termed as inability to use the available memory.
In such situation processes are loaded and removed from the memory. As a result of this, free holes exists to satisfy a request but is non contiguous i.e. the memory is fragmented into large no. Of small holes. This phenomenon is known as External Fragmentation.
Also, at times the physical memory is broken into fixed size blocks and memory is allocated in unit of block sizes. The memory allocated to a space may be slightly larger than the requested memory. The difference between allocated and required memory is known as Internal fragmentation i.e. the memory that is internal to a partition but is of no use.
Paging
A solution to fragmentation problem is Paging. Paging is a memory management mechanism that allows the physical address space of a process to be non-contagious. Here physical memory is divided into blocks of equal size called Pages. The pages belonging to a certain process are loaded into available memory frames.
Page Table
A Page Table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual address and physical addresses.
Virtual address is also known as Logical address and is generated by the CPU. While Physical address is the address that actually exists on memory.
Segmentation
Segmentation is another memory management scheme that supports the user-view of memory. Segmentation allows breaking of the virtual address space of a single process into segments that may be placed in non-contiguous areas of physical memory.
Segmentation with Paging
Both paging and segmentation have their advantages and disadvantages, it is better to combine these two schemes to improve on each. The combined scheme is known as 'Page the Elements'. Each segment in this scheme is divided into pages and each segment is maintained in a page table. So the logical address is divided into following 3 parts :
1. Segment numbers(S)
2. Page number (P)
3. The displacement or offset number (D)
