PHYSICAL AND VIRTUAL MEMORY

PHYSICAL AND VIRTUAL MEMORY

Physical Memory

Physically, memory is a collection of integrated circuits (ICs) that store data and program information as patterns of 1s and 0s in the chip. Physical memory can be split into two main categories:

volatile and nonvolatile.

Volatile memory loses any data as soon as the system is turned off; it requires constant power to remain viable. Most types of RAM fall into this category.

Nonvolatile memory does not lose its data when the system or device is turned off. A number of types of memory fall into this category, the most familiar is ROM but Flash memory storage devices such as Compact Flash or Smart Media cards are also forms of nonvolatile memory.

Virtual Memory

Most computers today have something like 32 or 64 megabytes of RAM available for the CPU to use. Unfortunately, that amount of RAM is not enough to run all of the programs that most users expect to run at once.

For example, if you load the operating system, an e-mail program, a Web browser and word processor into RAM simultaneously, 32 megabytes is not enough to hold it all. If there were no such thing as virtual memory, then once you fill up the available RAM your computer would have to say, "Sorry, you cannot load any more applications. Please close another application to load a new one." With virtual

memory, what the computer can do is look at RAM for areas that have not been used recently and copy

them onto the hard disk. This frees up space in RAM to load the new application. Because this copying happens automatically, you don't even know it is happening, and it makes your computer feel like it has unlimited RAM space even though it only has 32 megabytes installed. Because hard disk space is so much cheaper than RAM chips, it also has a nice economic benefit. So Virtual Memory can be defined as Part of Hard disc that is used as RAM is known as virtual Memory. This is generally done by OS to compensate for shortage of RAM.

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