Laptop RAM upgrade.

[SubScape]

I'm looking to buy 2 x 4GB sticks for my sister's Packard Bell laptop, at the moment it's 2 x 2GB pc6400 DDR2 sticks.
The question I have is can I is whether I can just buy 1 x 4GB stick and put it alongside and if this will work. Or whether it's recommended to get 2 x 4GB sticks.
Also this laptop will probably be used for a while so will 8GB be noticeably faster than 6GB + is is worth spending the extra on?
I'm also assuming she'll have a 64 bit version of Win 7 as the laptop came with 4GB. Thanks.

 

[Surveyor]

Check what version of Windows it has.

Right click on "Computer" and select properties.

Under "System" it will say if it's 32 or 64 bit.

The laptop may only have 2 RAM slots so you need to check that before making any decisions.

You also need to check the laptop supports more than 4GB.

Looking on OcUK a single DDR2 4GB SODIMM (I assume that's what it takes) costs £71.99.

It could be a very expensive upgrade for probably little difference in performance unless the laptop is being used for RAM intensive tasks.