What is vertual memory?

virtual memory

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.