Q: why is my mac running so slow?

A TB is a terabyte, but that doesn't apply to RAM. You buy RAM in gb (gigabyte) sizes. If the Crucial site is a problem, go to Macsales and see what that comes up with.

You may want other opinions, but mine is in my second to last post - as much as the Mac will take/or as much as you are happy to pay for. Maximising the RAM will make using Mountain Lion a much better experience.

If you have two 1gb chips at the moment, consider replacing those and filling all your slots with fresh matched RAM. Keep the 1gb chips as a backup plan if you have any problems with your new RAM, which I doubt you will, if you buy from the suggested sources.

Get the RAM from OWC.

Install two 4 GB (GigaByte) RAM modules to install the max. RAM amount of 8 GBs.

Here's is the complete set/pairs of RAM you need to order and install.

http://eshop.macsales.com/item/Other%20World%20Computing/8566DDR3S8GP/

And here is how to install it, here.

http://support.apple.com/kb/HT1423?viewlocale=en_US#2

Great - Mountain Lion will enjoy its new RAM .

Had same problem with my intel iMac and being slow - Memory - added memory and all worked fine -

You will be much happier with your new ram. Whoever advised you to upgrade to ML before addng ram gave you bad advice. Make sure you look at the installation videos either on the MacSales site or iFixIt.com or even youtube to make sure you know what you're doing. It's a very easy installation that can be done by a computer novice but the videos will help you with the confidence to do the job.