I have a dual channel RAM question.

[HomeAppraiser]

My sons computer has a socket 939 GeForce 6100 mATX NForce4 motherboard with 4 RAM slots. It came with 2x256 DDR400 and I would like to bump it up to 1GB. If I put a single 512mb DDR400 in the thrid or fourth slot will it slow down the existing dual channel RAM?

 

[RichUK]

By default, all ram will run at the same speed and latency (memory timings) as the lowest performing stick installed, defaulted by the BIOS. So if the 512 stick has better SPD timings it will be forced to run the same timings as the slower 256 sticks, or vice versa.

 

[HomeAppraiser]

OK but is dual channel all or nothing? Will the single stick in slot 3 interfere with the dual chanel RAM in slots 1 & 2?

 

[RichUK]

Originally posted by: HomeAppraiser
OK but is dual channel all or nothing? Will the single stick in slot 3 interfere with the dual chanel RAM in slots 1 & 2?

Sorry i dont quite understand that.

Dual channel will not be effected. you can have any arrangement you like. It just means one memory controller will be addressing to more memory than the other.

A 32bit processor can address to 4GB's of memory. You can have any arrangement you like within the four DIMM slots on the motherboard. Dual channel basically only offers a theoretical doubled bandwidth due to two seperate memory controllers, so you would be looking to use both channels if you have more than 1 stick of ram, as you do. In your case one channel is going to have more memory available, if you leave the current sticks where they are now.

I would perhaps stick both the 256 sticks in one channel and the 512 stick in the other channel. Look in the motherboard manual to make sure you use the right DIMM slots. If you are certain that you are running dual channel now, then remove one of the 256 sticks and place it in slot 3, then place the 512 stick in the previously occupied slot.

Channel A

Slot 1: 256MB stick
Slot 3: 256MB stick

Channel B

Slot 2: 512MB stick
Slot 4: Unoccupied


Make sure that the different memory channels do use these DIMM slots though, as some motherboards use slots 1 and 2 as the first channel and slots 3 and 4 as the second channel.

 

[Lord Evermore]

You have to have matching amounts in the slots in order for dual-channel to operate. As far as I know, with current chipsets you can't do something like having 2x256 in one channel, and 1x512 in the other channel, which would mean equal amounts of memory in each channel but wouldn't necessarily be addressable the same way. (With the old nforce2 you could do it that way, which allowed 3 slot boards to still use dual-channel.)

 

[Lord Evermore]

Originally posted by: RichUK
It just means one memory controller will be addressing to more memory than the other.

There's only one memory controller with current chipsets, which can operate in either 64-bit wide mode, or 128-bit wide mode. It can't work in dual-channel 128-bit wide mode with different amounts of memory in each channel, the way the nforce2 did, which did actually have 2 controllers which could operate semi-independently and wasn't actually operating in 128-bit wide mode.

 

[RichUK]

Originally posted by: Lord Evermore

Originally posted by: RichUK
It just means one memory controller will be addressing to more memory than the other.

There's only one memory controller with current chipsets, which can operate in either 64-bit wide mode, or 128-bit wide mode. It can't work in dual-channel 128-bit wide mode with different amounts of memory in each channel, the way the nforce2 did, which did actually have 2 controllers which could operate semi-independently and wasn't actually operating in 128-bit wide mode.

Yeah but this is socket 939 where the memory controllers are on the cpu die and not on a chipset. And s939 does indeed have 2 64bit memory controllers which are not effected by mis matched pairs.

EDIT: Actually i think the new AM2 chips have dual 64bit memory controllers, and s939 had a single 128bit memory controller. I'll have to check up. If this is the case OP, then go with what has been suggested and make sure there is equal amounts in each channel.

 

[HomeAppraiser]

At this point I am thinking that the extra 1x512mb added to the existing 2x256 will outweigh loosing dual channel.

More RAM > dual channel

At least until I can find an affordable 2x256 or 2x512 dual channel pair to add to the existing RAM.

Thanks.

 

[Lord Evermore]

In most cases getting two modules to equal the amount you want costs about the same, often less, than buying it all in a single module. $52 shipped for the cheapest 2x256 PC3200 modules on Newegg, $50 for the cheapest single 512MB module.

 

[Lord Evermore]

Originally posted by: RichUK
Yeah but this is socket 939 where the memory controllers are on the cpu die and not on a chipset. And s939 does indeed have 2 64bit memory controllers which are not effected by mis matched pairs.

EDIT: Actually i think the new AM2 chips have dual 64bit memory controllers, and s939 had a single 128bit memory controller. I'll have to check up. If this is the case OP, then go with what has been suggested and make sure there is equal amounts in each channel.

I'm looking at AMD's site now, I was going to ask you to give some documentation links. This page just says AM2 has a 128-bit interface, while S939 supported 64-bit or 128-bit, but doesn't specify that that means it was actually two separate 64-bit controllers, and they don't have any easily found information (and after a certain point, things can get too technical even for me). I've never seen it mentioned anywhere that any A64 had two controllers. Since you can still run an AM2 system in single-channel mode, it would seem odd for the controller layout to be radically different from s939's. Although since the first A64's were single-channel, it might make sense that the next step was just putting two of them in there, then for AM2 moving to a single 128-bit controller.

 

[HomeAppraiser]

All my other computers have 2x512 DDR333 and I have an extra 1x512 DDR400 laying around so that's what I have to use for now.