I know this is a stupid question but...

I got a Dell dimension c521. It is slow so I figure I should add memory.
There are 4 memory slots with 2 being used. How much memory is that? Well,
the cards that are in there say it they are  two cards with 1024 mb apiece.
 'free -h' reports

free -h
                   total       used       free            shared    buffers
  cached
Mem:          1.9G       1.4G       489M        18M        59M       535M

isn't 1024 one gig? Where is the rest?

SHould I buy this?

NEW 4GB 4x1GB DDR2 PC2-5300 667MHz RAM Memory for Dell Dimension C521
<http://www.amazon.com/4x1GB-PC2-5300-667MHz-Memory-Dimension/dp/B00KFND9SC/ref=sr_1_1?s=electronics&ie=UTF8&qid=1412798813&sr=1-1&keywords=dimension+c521+memory>

or should I get this?

2GB (2x1GB) RAM Memory CMS Compatible with Dell Dimension C521 Desktop
<http://www.amazon.com/Compatible-Dell-Dimension-C521-Desktop/dp/B00BL30RZS/ref=sr_1_3?s=electronics&ie=UTF8&qid=1412798813&sr=1-3&keywords=dimension+c521+memory>
:-)~MIKE~(-: