where can i buy additional RAM for a desktop (Dell i7) that i acquired recently
Ebay or a computershop..
Make sure you buy the right kind for your desktop
Dell i7 is not enough info. I googled for that and got swamped with different answers. Got a model number? You could try PC Case Gear or CentreCom or Scorptec.
it requires a DDR3.
google CPU-Z. run it and it will tell you your memory spec/setup.
Alternatively use windows computer management to see what memory, how many slots etc. Then you can match (if you have 1 Ram stick) with one of the same spec (manufacturer not important) to get dual channel running.
the best way is to open the case, look at the model of the RAM on the stick.
and google the model to see the spec. or google the store that sells the same model