Single Channel Dual Channel.. What the hell???

[maury73]

You can't run a 256 and a 512 in dual channel, it doesn't work at all!

If you ipotetically could do a thing like this, passing the 512MB barrier (2x256) would lead to errors, because the RAM controller can't switch the bus width on the fly: it runs always at 64 bit or always at 128, it can't do a thing like you wrote, it is a non-sense.

I spoke of a setup of 2x512 + 1x1GB or 2x256 + 1x512: as I said the total memory amount of the two channels *MUST* match.

 

[maury73]

There is no proof to provide, we do not use silly tools like CPUZ or similar, we write out own FW and also design our own boards for our purposes, so we verify the RAM controller operation with logic analyzers because BIOS and software reports are often erratic with strange configurations.

However speaking of standard commercial mobos We tested the Asus A8N and the MSI K8N with standard BIOS FW and they work with theese two configurations:

2x256MB CH0 + 1x512MB CH1
2x512MB CH0 + 1x1GB CH1

Strangely they don't work if you exchange the two channels, putting the odd modules in CH0.
I don't know if other mobos work like theese, you must try, but the 3 modules must have the same speed and timings capability.

If I understood well your first post you have a 2 slots only mobo, so it is much better for you to use the 2 identical modules and go dual channel: no mobo at all can work with 512MB on CH0 and 1GB in CH1, this is impossibile, even changing the BIOS.

 

[maury73]

If the POST tells you that the memory runs in dual channel it is right, I never seen errors in this. The errors usually regards frequency and timings, but dual/single channel mode was always reported correctly by POST in all the mobos I've seen.

If you are still in doubt you can use a benchmark program (the good old memtest86 is perfect in this!): doing a RAM bench you can tell if you are running in dual channel by the bandwidth reported.

 

[maury73]

Sorry, but you are wrong in a thing: it's a non-sense to say that "the third stick is a normal sitck", all the sticks are normal!
As I said the sticks are all identical, they do not know what dual channel is, it is the RAM controller that address them in dual or single channel mode: we have designed and tested a system board for Texas 6600DSP with a Quad Channel DDR2 controller using standard Kingstom 1GB modules.
It's a controller issue only the capability to drive the modules in dual channel or not.

The AMD integrated controller is able to run 3 modules in dual channel, you can read this in the official AMD Datasheet (you can found the document on the AMD website). All that matters to the controller is the total RAM amount of the two channels that must be identical, as in the 2 example configurations I mentioned.

But the BIOS also must support theese strange config, because it is BIOS responsibility to read and process the modules SPD and program the AMD RAM controller accordingly.

So it depends on two factors: RAM controller (the AMD one can do that) and the BIOS, and this is a mobo related factor.

 

[maury73]

I repeat this works on A8N (normal, SLI not tested) and K8N: double or single sided doesn't matter for a well written BIOS FW it is only a PCB related and chip availability thing to use single or double sided modules.

My modules are double sided and work, but as I said it depends on mobo FW: as an example it works for me on the A8N, but doesn't work on the A8V.

 

[maury73]

I think you made a wrong assumption: the 2 512MB modules have to be mounted on the same channel, making a total of 1GB on one channel, equals to the single 1GB module mounted on the other channel.

Let you have a 4 slot mobo: 0 & 1 on CH0, 2 & 3 on CH1.
If you put two 512MB modules on slots 0 & 1 they'll use the 64bit bus of CH0 and will be addressed in sequence (there are dedicated address decoders on RAM controllers that do this): they will be concatenated in a unique contigous array of 1GB.
This is how *ANY* memory bus works, not only the PC ones.

The two channels are 64 bit each, no matters how many modules you put in the slots. Obviously the BIOS FW must be able to program the address decoders in the right way in order to access the modules in the correct way: the majority of them (like Via) will disable dual channel operation if they found different number of modules per channel, regardless of their size.

And there is an explanation for this: the very first DDR mobos only had 3 slots, because of problems in PCB traces and bus drivers that did not garantee signals integrity with 4 slots. With theese mobos you could only use 2 modules in dual channel or 3 in single channel, because of trace delays problems.
Many BIOSes are still inherited from this old stuff, thus not allowing the 3 modules configuration.

As I said many times, it is only related to the BIOS FW ability to correctly recognize the RAM configuration and properly program the RAM controller and this is not an easy issue: SPD data aren't standard at all and many SPD chips contain wrong parameters (as reported in many articles by TomsHardware itself!) and this is why, in our image processing system boards, we often reprogram the SPD chip with new correct values.

 

[Anoobis]

I will soon have access to an Abit KN8 SLI, 2x512MB DDR PC3200 and 2X1GB DDR PC3200.

I will test the idea and run the 2 512s in CH0 and 1 of the 1 GB in CH1 to see if it works in dual channel and report back on the matter.

Forgive us yanks, but what's a lorry?

 

[Anoobis]

Ohh, thanks. I figured that's what you were talking about, but wanted to be sure.

We have several terms. Semis ( 😳 ), tractor trailers, diesels, big rigs.....

When I used to work for NCR, some of our ATMs came out of Dundee. We had a few design problems and some of your Dundee boys had to come out and give us a hand. I quickly learned the terms torch, spanner....

However, if it wasn't for the young guy that came with them, I would never have known what the older guys were saying. Apparently it was english, but...damn. Hah, I'm sure they probably said the same thing. The younger guy was more in tune with American culture and had to act as a translator.

 

[Anoobis]

NO....I really thought he wanted a blowtorch!!

I remember the first time one of the older dudes spoke to me.

Ughh klook bok duuk thouhg!

My eyes glazed over with that deer in the headlights look. Then it dawned on me...the man was a Klingon.

Actually, he just wanted to know where the restroom was.

 

[Anoobis]

Bog may have been somewhere in that phrase. It was back in 2000, so it's hard for me to remember. Hell, I remember when I didn't know what the "head" was when someone referred to it instead of the restroom (that was back in ole 95).

As I noted before, I will be getting my hands on some new (well new to me) equipment and should have something up and running for testing by this weekend. I'll post my results if I have time to get to it.

 

[bombasschicken]

back on subject i still want to see proof of this tri-channel memory solution this guys is going on about. its the only term i can come up with to explain how three sticks can work in dual channel mode. i have never heard of this. the scary thing is he might be telling the truth and everyone on these boards have benn telling lies all this time 8O

i kinda understand the concept of dual channel now.. so it makes sense for 2 sticks only.. however why would they intentioally make a dual channel board with only 3 slots? unless its possible to have the tri-channel thingy... although i could be wrong...

 

[Zoness]

...said this once in another thread....will say it again here, repeat after me...

There is no such thing as dual channel memory. It is the chipset/mobo that supports dual channel - any memory that fits into that chipset/mobo, will run in dual channel if you put the 2 sticks into the proper slots.

As long as you fit similar memory into the right slots, it will work?

Say I get another Kingston ValueRAM 512MB stick of RAM, same one I got in now, If I put it in the other slot for dual channel then it will work properly?

 

[bombasschicken]

ok.. so help me figure this one out...

i decided to test the two better configs.. the 2gigs and the 1.5 @ (what the bios says) 400mhz

my real world test, being that i am mostly using this machine for gaming, is a FPS test in doom3.. the "timedemo demo1 usecache" thingy.. so i ran the test in both situations..

ok now everyone says use the matching pair of 2 gigs.. however...

when i use the 2gigs i get 58.9FPS
when i use the 1.5gb i get 62.8FPS

I ran this test 3 times on each config, defraged, and a restart between..

yes i know this is not real benchmarking but this is how i like to figure the best configs...

and i know its only 4FPS but its still better for some reason..

so what do you guys think?