If your computer is running slowly, it may need more memory.  As applications (including your web browser) become more sophisticated, they use up more memory, and start bogging down your computer.  You can buy memory from the computer manufacturer, but you can save lots of money by buying directly from the memory manufacturer.  Crucial Technology
offers excellent pricing on guaranteed-compatible memory, with a great widget that will scan your system to find the memory you need, and a 10% discount when you click from this link.