Looking at a PC system (Dell) and spec is perfect other than it only has 256mb of RAM.... I wanted 512mb of RAM.... Now Dells site is rather confusing to me when I looked to see how much it would be to increase my RAM.... I was under the impression you have to add an identical RAM to increase, ie I have 256mb so add another 256 to = 512....

Dells site lists them like so;

DELL - 256MB DDR333 Dual Channel Memory (2x128) for Dimension 4600 MMT
Dell Part : 370-11355, Manufacturer Part : 370-11355
Usually Ships: 5-7 Days £77.55
£59.93
[You Save £17.63]


DELL - 512MB DDR333 Dual Channel Memory (2x256) for Dimension 4600 MMT
Dell Part : 370-11356, Manufacturer Part : 370-11356
Usually Ships: 5-7 Days £171.55
£130.43
[You Save £41.13]

So I don't get it.... Which one do I need? as the 512 is 2x 256 but I already have 1x 256

So I need help fast as I would like to buy this system, but not if it gonna cost another £130 to upgrade the RAM Cos then the price ain't worth it