Assuming that you're running Windows, go to start, then programs, then accessories, then system tools, then disk clean-up. This will remove unused files. Next, archive or compress seldom used files, then burn them onto a CD or DVD as back-up. Once you've done this, delete away all the archived files that you've saved onto the CD. Finally, defragment your hard drive to maximize efficient use of your drive.
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If only you knew the power of the Dark Side of the Force
Also : Internet use accumulate a lot of temp files and if your retention period is too long it will eat disk space. Go to settings and reduce the time.
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Never do today what you can put of until tomorrow - Student motto
Use a tool like procexp from sysinternals (http://ask-leo.com/d-31017a
) and use it to see who is using memory, how much, and then watch to
see how it changes over time.