Dual Channel Memory on S939 Board

[phoenix198]

I've just recently built a S939 based system using an ECS NForce4-S939 with a Athlon X2 4400 S939 (obviously!). I have installed Vista Home Premium and everything in the garden is rosy with one exception:

I have 2 x 1GB sticks of PC3200 DDR installed in DIMM slots 1 and 2 but the system seems to be under-performing; boot screens show memory databus running at 64-bit rather than 128-bit, and Vista Experience Index only 4.4 for memory performance - the other elements are all over 5.0.

I realise that this is no doubt because the two 1GB sticks are not a matched pair - one is a Crucial product and the other 'brand X'. However I also have a pair of matched 512MB PC3200 DDR sticks from Crucial, although these are not yet installed.

My question is this; would I get improved memory performance and a higher Windows Experience Index by replacing the 2 x unmatched 1GB sticks running in single-channel 64-bit mode with the two matched 512MB sticks running in dual channel 128-bit mode?

(Sorry to pose a theoretical question to the forum when it might seem simpler to physically perform the change and find out myself, but I recently ruptured my Achilles tendon and am in plaster from toe to groin, so rooting around under my desk and doing so isn't quite as straightforward as I would like!)

[Sprite]

My question is this; would I get improved memory performance and a higher Windows Experience Index by replacing the 2 x unmatched 1GB sticks running in single-channel 64-bit mode with the two matched 512MB sticks running in dual channel 128-bit mode?

I doubt it, with Vista you'll want all the RAM you can get.

Is the 64-bit thing not an option in the BIOS ? T1 and T2 ?

[phoenix198]

I doubt it, with Vista you'll want all the RAM you can get.

Is the 64-bit thing not an option in the BIOS ? T1 and T2 ?

I've had a pretty thorough poke through and tweak with the BIOS settings to no avail, so I'm fairly sure that the 64-bit thing is being caused by the mis-matching RAM modules.

Take your point about Vista's hunger for RAM, though.

[hibby]

Erm, are you sure that dual channel mode isn't achieved by putting sticks in DIMM slots 1 and 3? Not having read the manual myself I wouldn't know, but that's what I had to do on my (totally different) motherboard.

And as far as I know, mismatched pairs doesn't prevent dual channel mode, it just might not go quite as fast.

[phoenix198]

Erm, are you sure that dual channel mode isn't achieved by putting sticks in DIMM slots 1 and 3? Not having read the manual myself I wouldn't know, but that's what I had to do on my (totally different) motherboard.

And as far as I know, mismatched pairs doesn't prevent dual channel mode, it just might not go quite as fast.

The memory Banks on the board are colour coded (Bank 0 lilac, Bank 1 purple) and I have assumed that slots 1 and 2 (lilac) are Bank 0, slots 3 and 4 are Bank 1. My motherboard manual isn't particularly clear about this (are they ever?) but the table in there definitely seems to say that a 128-bit databus requires that you put DIMMs in adjacent slots and that they both need to be 'single rank' or 'double rank' DIMMs.

With this and the Wiki article here that states that "A matching pair needs to match: - Capacity (e.g. 1024MB) - Speed (e.g. PC5300) - Number of chips and sides (e.g. 2 sides with 4 chips on each side)" I am fairly confident that have the DIMMs in th right slots for dual channel but that they are not a matching pair.

[scrandman]

You don't say exactly which nForce4 board it is, but having had a look at the ECS website, it looks like you are right on with the memory positions. Two adjacent slots of same colour will give you dual channel.

Dual channel really needs RAM which is either identical or very, very similar. I think your problem is the variation in the RAM you are using.

[phoenix198]

Thanks to all who replied.

Looks like the time for thinking about it is over and its time to crawl around under my desk!

[phoenix198]

Done the deed - replaced 2 x unmatched 1GB PC3200 DDR sticks in Bank 0 with 2 x Crucial matched 512MB PC3200 DDR sticks:

Boot screen now indicates that system is running in Dual-Channel 128-bit mode, and memory performance figure in Windows Experience Index dropped to 2.9 from 4.4!

I guess that answers that question, then!

[scrandman]

Certainly with old Athlon XP systems, dual channel meant little in terms of real-life performance (~5%). Not sure if the same figure applies to S939 systems, but in terms of real-life performance there was little between equivalent S754 (single channel) and S939 (dual channel) systems.

With a memory hog like Vista, more is much definately better. Win XP for me - 1Gb purely to run an OS is too much IMHO.