v VIRTUAL MEMORY
· Virtual Memory is a storage scheme that provides user an illusion of having a very big main memory. This is done by treating a part of secondary memory as the main memory.
· In this scheme, User can load the bigger size processes than the available main memory by having the illusion that the memory is available to load the process.
· Instead of loading one big process in the main memory, the Operating System loads the different parts of more than one process in the main memory.
· By doing this, the degree of multiprogramming will be increased and therefore, the CPU utilization will also be increased.
v WORKING
· In modern word, virtual memory has become quite common these days. In this scheme, whenever some pages needs to be loaded in the main memory for the execution and the memory is not available for those many pages, then in that case, instead of stopping the pages from entering in the main memory, the OS search for the RAM area that are least used in the recent times or that are not referenced and copy that into the secondary memory to make the space for the new pages in the main memory.
· Since all this procedure happens automatically, therefore it makes the computer feel like it is having the unlimited RAM.
v Types of Virtual Memory
In a computer, virtual memory is managed by the Memory Management Unit (MMU), which is often built into the CPU. The CPU generates virtual addresses that the MMU translates into physical addresses.
· There are two main types of virtual memory:
o PAGING
o SEGMENTATION
v Advantages of Virtual Memory
1. The degree of Multiprogramming will be increased.
2. User can run large application with less real RAM.
3. There is no need to buy more memory RAMs.
v Disadvantages of Virtual Memory
1. The system becomes slower since swapping takes time.
2. It takes more time in switching between applications.
3. The user will have the lesser hard disk space for its use.
v Virtual Memory vs Physical Memory
· When talking about the differences between virtual memory and physical memory, the biggest distinction is speed. RAM is much faster than virtual memory, but it is also more expensive.
· When a computer needs storage for running programs, it uses RAM first. Virtual memory, which is slower, is used only when the RAM is full.
Feature
Virtual Memory
Physical Memory (RAM)
Definition
An abstraction that extends the available memory by using disk storage
The actual hardware (RAM) that stores data and instructions currently being used by the CPU
Location
On the hard drive or SSD
On the computer’s motherboard
Speed
Slower (due to disk I/O operations)
Faster (accessed directly by the CPU)
Capacity
Larger, limited by disk space
Smaller, limited by the amount of RAM installed
Cost
Lower (cost of additional disk storage)
Higher (cost of RAM modules)
Data Access
Indirect (via paging and swapping)
Direct (CPU can access data directly)
Volatility
Non-volatile (data persists on disk)
Volatile (data is lost when power is off)
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