Minecraft running astoundingly slow?!

My computer has been running Minecraft very slowly. When I play, I often only get 1-3 fps. It is very annoying.

I have a 64bit Windows 8 computer with 4GB of RAM and it runs decently fast.

I have tried turning off particles, changing graphics to fancy, and every other trick in the book, but I only get a few fps more/ How can I get my fps up to 20-40 without downloading a shitload of complicated things?

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