You computer continually stores information as you use it. By doing so it can quickly "reference" files that you have created rather than having to create them all over again. For example the first time you visit a website your computer has to download all the images in order to view them. Copies of these photos are cached so that next time you go to that same website, the images are already available.
This is a very basic explanation and there are plenty of people who can explain this in much greater detail, but that is why in a nutshell.
Hello all:
I just bought a HP laptop installed with window7 home premium. At the beginning, the size of OS is about 30G.(It means That HP installed many Adverts)
To my surprise, After two weeks the size of C: becomes 60G. Why the used space is becoming so big? What occupys the space of the hard disk? --Zhao

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