Adding memory questions - still confused after reading up.

I would like to add some memory to my not so new system and would like help. I think I put myself in a corner with earlier, ill-informed purchases. I have 3GB RAM now, 2 more should suffice for my use (linux, lots of windows/apps/tabs open but no games etc.)
Thank you for any input - I did read up on this but remain confused.

Really short version: Can I mix these in adjacent slots?
DDR2 800 2GB 4-4-4-12 2.1V
DDR2 800 2GB 4-4-4-12 2.0V

The longer version: I have 4 DDR2 800 slots, ABIT says 8GB max, I have a matching pair of 512MB modules and a single 2GB module (full details of system below). Neither latencies nor voltages match between the 2GB and the paired 512MB modules.

I've read that you can mix latencies, they just run at the longest latency, but that mixing voltages is the problem. I also read that you need a pair to run in dual channel mode, otherwise they run in slower single channel mode. However, I can no longer find a single module that matches the 2.1 voltage of the 2GB.

Can I use a 2.0V 2GB in the matching slot with the existing 2GB module if the latencies match, as asked above?
Would I be better off just swapping out the 2x512 for a matching 2 x 2GB modules? I know I'd be better total memory, but I don't need that much more and the cost really matters, plus I'd still have that slow single 2GB module (if I understand correctly)

I'd prefer to buy from NE but am open to suggestions.

Searching only for DDR2 800 (and up) and 2.1V only gives one result, a 4x2GB set for ~$140, more than I have.
When I instead search only for DDR2 800+ and Cas 4 gives more results, for example:
$34 Kingston HyperX 2GB DDR2 800, Cas 4, 2.0V, 4-4-4-12
Or
$64 G.SKILL 4GB (2 x 2GB), Cas 4, 2.0V - 2.1 V, 4-4-4-12

The 2GB PatriotPatriot Extreme Performance 2GB 240-Pin SDRAM DDR2 800 Desktop Memory Model PEP22G6400LL, Cas 4, 4-4-4-12, 2.1V

Details:
MB: ABIT NF-M2 nView AM2 NVIDIA GeForce 6150 Micro ATX AMD
updated bios (current -1)
MB Memory specs:
4×240pin
DDR2 800
Dual Channel
ABIT lists max as 8GB

I first purchased
2 X Wintec AMPO 512MB 240-Pin SDRAM DDR2 800 3AMD2800-1G1K-R (part number is for both sticks as kit)
Cas: 5
Timing: 5-5-5-12 (I thought Cas = first number here?)
Voltage: 1.8V

I later added
1X Patriot Extreme Performance 2GB 240-Pin SDRAM DDR2 800 Desktop Memory Model PEP22G6400LL
Cas: 4
Timing: 4-4-4-12
Voltage: 2.1V (according to what is on module's label and Patriot's website, though newegg says 2.2. I'll go with 2.1V)

In case it matters:
CPU: AMD Athlon 64 X2 3800+ Windsor 2.0GHz Socket AM2 65W
HDs: WD 250GB, Samsung 1TB, Seagate 1TB
No overclocking, plenty of swap space, no raid. Have added compcache and tuned swappiness, was thrashing like crazy past month. Expect to keep this computer for a few more years but any RAM I buy will not be usable on next one, of course.

Again, thank you - even more so if you made it this far!

you CAN mix and match voltages, bear in mind you run the risk of burining out the lower voltage chips

4 X 240-pin DIMM sockets support max. memory capacity 8GB

so your best bet would be 4x2gb ddr2 800MHz ram

http://www.newegg.com/Product/Prod [...] 6820231207
thats the cheapest i could find off hand

http://www.amazon.com/Corsair-VS4G [...] 23&sr=1-97
This set is $51.99 and has free shipping.

http://www.amazon.com/Komputerbay- [...] 1&sr=1-110
This set is $42.00

G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model F2-6400CL4D-4GBPK
$64.99
http://www.newegg.com/Product/Prod [...] 6820231148

This set would be a match for the patriot memory that you already have. You said that you were running Linux? Is there a 32bit and 64bit versions of linux and does it treat ram the same way asa windows? 32 bit only sees 4gb of ram and 64 bit sees all the ram?

Thank you for the responses - I was away for a few days.
I think I need to understand what voltage effects. If I recall correctly (without rebooting and checking the bios options) I can change the voltage and timing options for the memory in bios. Can I set the voltage to the lower?

Perhaps a better question is Does the voltage difference matter across all four slots, or just for each pair? If I have the single 2.1 volt 2GB module in one slot, then a matching pair of lower voltage modules in the other 2 slots does the difference matter?


I'm running 64 bit linux, though there are pretty common ways of working around the 4 GB limit for 32 bit linux. I think you have to use the PAE kernel module, don't recall details as I've never had to do it.

Thanks!

Kingston HyperX 8GB (4 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Quad Kit Desktop Memory Model KHX6400D2LLK4/8G
$139.99
http://www.newegg.com/Product/Prod [...] 6820104108

G.SKILL 8GB (2 x 4GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Desktop Memory Model F2-6400CL5D-8GBPQ
$159.99
http://www.newegg.com/Product/Prod [...] 6820231301

KOMPUTERBAY 8GB ( 2 X 4GB ) DDR2 DIMM (240 PIN) 800Mhz PC2 6400 PC2 6300 with Heatspreaders 8 GB - CL 5
$117
http://www.amazon.com/KOMPUTERBAY- [...] 69&sr=1-38

Komputerbay 8GB (2 X 4GB) DDR2 DIMM (240 pin) 800MHZ PC2-6400 PC2-6300 8 GB KIT with Crown Series Heatspreaders for extra Cooling CL 5-5-5-12
$123
http://www.amazon.com/Komputerbay- [...] 10&sr=1-68

Komputerbay 8GB 2X 4GB DDR2 800MHz PC2-6300 PC2-6400 DDR2 800 (240 PIN) DIMM Desktop Memory
$110
http://www.amazon.com/Komputerbay- [...] 8&sr=1-119

Here are some choices to look at and some may be kind of high and others are a little more reasonable but DDR2 is hard to find and is more expensive than DDR3.