Virtual memory is a feature of an operating system (OS) that allows a computer to compensate for shortages of physical memory by temporarily transferring pages of data from random access memory (RAM) to disk storage
.
Virtual memory combines your computer’s RAM with
temporary space on your hard disk. When RAM runs low, virtual memory
moves data from RAM to a space called a paging file. Moving data to and
from the paging file frees up RAM so your computer can complete its
work.
The more RAM your computer has, the faster your
programs will generally run. If a lack of RAM is slowing your computer,
you might be tempted to increase virtual memory to compensate. However,
your computer can read data from RAM much more quickly than from a hard
disk, so adding RAM is a better solution.
The total amount of RAM (Random Access Memory) installed might not always be sufficient
to run all the applications on the system. Windows memory management implements
and manages what is called Virtual Memory. It’s the method of extending the available physical
memory on a computer. PageFile is a file on disk which is used to swap physical
memory pages to and from a disk. Virtual
Memory comprises of total available physical memory(RAM) on the computer and
size of the PageFile on disk.
vertual memory manager
Virtual Memory Manager is
responsible for mapping physical memory and virtual address spaces for a process.
It keeps track of each mapping for VAS addresses using a page table, and the mapping information
itself is stored in a Page Table Entry (PTE). The PTE is 4K in size and shares
the same space as other system information and structures of the system.
Already for a long time users encountered the problem of placement in
the program memory, the amount exceeding the available free memory. The
decision was splitting program at the part called overlay. Zero overlay
began to run first. When he finished his performance, he caused another
overlay. All overlays stored on the disc and shifted between memory and
disk operating system tools. However, the program broken down into
parts and upload their planning in the OP had to make programmer.
The development of methods of computational process in this area led
to the technique known as virtual memory. Virtual called resource to
users or user programs submitted owning properties, which it does not
have in reality. For example, the user may be provided virtual OP, the
amount of which exceeds all available in real OP. User program writes as
if in its possession available homogeneous OP large amount, but in
reality, all data used by a program stored on one or more different
types of MY course on discs, and if necessary parts are displayed in
real memory.
Virtual memory (CAP) – a combination of software and
hardware that allow users to write programs whose size exceeds the
available OP. For this EP solves the following problems:
– VM places the data into different types, such as part of the program in the OP, and some on disk;
– Moves as needed between CL data of various types, such as downloads of the desired program from the disc in the OP;
– Converts virtual addresses into physical.
