Answer is C
The pc will have insufficient amount of memory when most of its memory is already occupied. WHY THIS HAPPENS? many reasons, like
1)OS is consuming more RAM than available for instance, Vista minimum requirement is to have at least 1~2GB of RAM to operate fine unlike XP which needs much less
RAM. e.g. 128MB.
2)many applications are opened at the same time. and there is no enough space on RAM.
3)virus or spyware
And the pc must use virtual memory if there were no such thing as virtual memory, then once you filled up the available RAM your computer would have to say, "Sorry, you can not 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
The read/write speed of a hard drive is much slower than RAM, and the technology of a hard drive is not geared toward accessing small pieces of data at a time. If your system has to rely too heavily on virtual memory, you will notice a significant performance drop. The key is to have enough RAM to handle everything you tend to work on simultaneously
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