How does virtual memory use disk space for RAM?

Virtual memory uses disk space as an extension of the computer's RAM, storing inactive data and applications.

Virtual memory is a memory management technique where secondary memory can be used as if it were a part of the main memory (RAM). When the RAM is not sufficient to hold all the programs and data, the operating system uses a portion of the hard disk space as virtual memory. This process is known as swapping, where data from RAM is moved to the hard disk to free up space.

The operating system divides memory into pages, small blocks of contiguous memory. When a program needs more memory, the operating system checks which pages in RAM have not been used recently and writes them to the disk. This creates room in RAM for the new data. The pages written to the disk are tracked in a page table, so they can be retrieved when needed.

When a program tries to access data that's not in RAM but in the virtual memory, a page fault occurs. The operating system then swaps a page of data from RAM to the disk, and the requested page from the disk to RAM. This process is invisible to the user and the programs, as they perceive the virtual memory as an extension of the RAM.

However, using virtual memory has a performance cost. Accessing data on the hard disk is slower than accessing data in RAM. Therefore, the operating system tries to minimise the use of virtual memory and keep as much data as possible in RAM. It uses algorithms to predict which pages are likely to be needed soon, and keeps them in RAM.

In summary, virtual memory allows a computer to run more programs or handle larger data than it could with RAM alone. It uses disk space to store data that doesn't fit into RAM, and swaps data between RAM and the disk as needed. Despite the performance cost, it's a crucial part of modern operating systems, enabling them to manage memory efficiently and provide a smooth user experience.