when i bought it 2nd hand, yes i installed my own RAM.
Well apparently it's been working, with three out of four slots filled with three identical 1GB 800Mhz memory cards and the remaining fourth slot holding what I guess is a 512MB 553Mhz (or a bit slower?) memory card.
However as I understand things, all of the memory would be SLOWED DOWN BY THE BIOS to conform to the slowest memory present. So I don't think you've been getting the performance you'd hoped for with those three "fast" cards. You've actually been getting the performance of those three cards limited by the slowest card, i.e. the 512MB fourth card.
Again, 800Mhz is faster than Dell says the machine can support... although apparently it's physically working. But this may be because you actually have that slow fourth card, so this may be what has "saved" you in the first place. Don't really know, but it's really not right.
My recommendation is to spend $64 and
buy this 2x2GB kit from Crucial which is guaranteed to be perfect for your Dell XPS E520, and which will be the proper 667Mhz faster memory that Dell states is supported by your machine.
Remove all four of your current memory cards, and place these two 2GB cards in slots 1 and 2 of the machine. This will give you the 4GB you want, in just two matched memory cards... and at the fastest speed Dell states can be used.
i have 2 questions?
1.In my case, is having 3GB RAM faster than 3.5GB?(i have a feeling that taking my 512mb ram out will be better)
I wouldn't spend much time trying to argue one way or another.
My honest recommendation is to spend $64 and be done with it. Toss your current four memory cards and replace them with the two new ones from Crucial. 4GB is better than either 3.5GB or 3GB. And, your machine's memory will actually be running at the max 667Mhz speed it can run at, rather than the 553Mhz it is currently probably running at because that's the slowest card of your four.
2.When i have 4 RAM slots, but only decide to use 3 slots leaving 1 remaining, is it faster? i heard my friend saying that if i use all slots, then the motherboard uses more effort.
Well.. "more effort" is not really an appropriate description.
But personally I would NEVER not use pairs of matched memory cards in pairs of memory slots. Also, I would fill either 2 or 4 memory slots, and never 3.
As Dell said:
DDR2 Memory Overview
DDR2 memory modules should be installed in pairs of matched memory size, speed, and technology. If the DDR2 memory modules are not installed in matched pairs, the computer will continue to operate, but with a slight reduction in performance.
