Focer font of knowledge, Refurbished PCs

[fazersharp]

I never knew that my laptop had two slots for RAM and only one was occupied with a 4GB board.
I just bought a refurbished 4GB board for £17, took the back cover off, slotted it into the empty space, and now have 8GB to play with. 

There can be limits and bottlenecks with the amount of ram that is actually recognised by your system as a whole. Depends on the motherboard and also the x32 or x64 operating system.

Sounds like I know what I am talking about ----- I don't fully so Im sure an expert will come along and help us all. 
Yours could of equally been occupied by x2 2gb cards. I always understood you had to add in pairs - as in- you could not add an 8 to a 2 card motherboard that already has a 4 in one slot, you should add another 4 to the vacant slot or replace both slots with a matching 8s =16 total or take em all out and just have x1- 16GB  :o :\ :uhuh :wall 
To further complicate things tower PCs can have 4 slots so you can go 4x4=16 or just use 2 and go 2x8=16  or even go 1x16.
My PC now has 16gb Ram. And a samsung evo ssd opends win7 in 30 seconds and closes in 9 seconds.