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Help with dual channel memory mode..

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November 21, 2007 1:22:53 PM


Hi,
I was wondering if anyone could help me with this issue. I have an (ASUS P5GD2X motherboard) with 4 memory DIMM slots, i want to fill all slots with 1Gb moduals =4Gb of ram, all of the same size and speed. in doing this, will all memory moduals then be running in dual channel mode?? I'm doing the research but am new to the world of memory, any tips..

Musicmad
November 21, 2007 4:38:33 PM

They should.
November 21, 2007 5:05:01 PM

Unless you are using a 64b OS then most if not all of you 4th slot will not be used so I would stick to two 1G sticks in dual channel.
Related resources
November 21, 2007 5:32:41 PM

It will run dual if your memory is dual. There isnt much difference at all between dual and single channel.
November 21, 2007 5:48:41 PM

roadrunner197069 said:
There isnt much difference at all between dual and single channel.
Very true, I was extremely disappointed when I benched my RAM in single channel and dual channel. Very little gain, certainly not even close to the doubling that it is supposed to get in theory.
November 21, 2007 7:02:03 PM

Zorg said:
Unless you are using a 64b OS then most if not all of you 4th slot will not be used so I would stick to two 1G sticks in dual channel.


What do you mean the 4th slot will not be used.. if i use only 2Gb moduals in dual mode, i will only have 2Gb of ram. i understand that (windows XP 32b OS) can not read 4Gb of ram, but still, i want to fill all slots with 1Gb moduals to get as much ram out as possible. so by filling all 4 slots with 1Gb moduals, what would be the maxium amout of ram i would expect to receive.
November 21, 2007 7:15:56 PM

musicmad said:
What do you mean the 4th slot will not be used.. if i use only 2Gb moduals in dual mode, i will only have 2Gb of ram. i understand that (windows XP 32b OS) can not read 4Gb of ram, but still, i want to fill all slots with 1Gb moduals to get as much ram out as possible. so by filling all 4 slots with 1Gb moduals, what would be the maxium amout of ram i would expect to receive.
I only glanced at this but it should answer your question. Ask Dan: What's with the 3Gb memory barrier?

November 22, 2007 1:08:02 PM

Zorg said:
I only glanced at this but it should answer your question. Ask Dan: What's with the 3Gb memory barrier?


Hi Zorg,

Thanks for the link, LAST QUESTION, in using all 4 moduals of 1Gb = 4Gb of Ram, i understand as you put it, i will not use most of the ram in the 4th modual. however in still doing this, would my system still run ok with 4 1Gb moduals installed?? would there be any compatibility problems??, or would it be that i would just lose.. most of the memory in the last modual??..


November 22, 2007 1:42:16 PM

musicmad said:
Hi Zorg,

Thanks for the link, LAST QUESTION, in using all 4 moduals of 1Gb = 4Gb of Ram, i understand as you put it, i will not use most of the ram in the 4th modual. however in still doing this, would my system still run ok with 4 1Gb moduals installed?? would there be any compatibility problems??, or would it be that i would just lose.. most of the memory in the last modual??..
If you want to use all 4 slots then you would want 2 1G and 2 512M sticks. Some mobos have problems with 4 sticks some don't. At a minimum, with 4 1G sticks you would have the first 2 sticks running in dual channel and the third stick not. The 4th stick would be mostly, if not completely be unused.
November 22, 2007 2:23:23 PM

from what I understand 32 bit can allocate only 4 GB of ram total. If you add a video card it takes away from the 4GB, a few other things use a few bits and bytes too (or a bit more even). For convenience everyone just assumes 3GB is the max for ram.

But if you really need more, won't a 64 bit system be more for you? I know it will cost more (isn't there an easy way to upgrade from 32 to 64, I think there should be a very cheap upgrade).
November 22, 2007 2:54:00 PM

4x1GB will run dual channel just as fine as 2x1024 + 2x512 will.

Dual channel and the lost ram is not related
November 22, 2007 3:08:06 PM

Memory addresses are spread out across all the modules. So you'll find a bit of lost ram sitting on top of all the modules.
November 22, 2007 3:47:31 PM

dengamle said:
Memory addresses are spread out across all the modules. So you'll find a bit of lost ram sitting on top of all the modules.
From my understanding there is some RAM that is mapped for legacy purposes but most of the RAM that is mapped for the newer VGAs etc. is between 3G and 4G. Do you have any links so I can see what you are talking about.
November 22, 2007 4:21:09 PM

Zorg said:
If you want to use all 4 slots then you would want 2 1G and 2 512M sticks. Some mobos have problems with 4 sticks some don't. At a minimum, with 4 1G sticks you would have the first 2 sticks running in dual channel and the third stick not. The 4th stick would be mostly, if not completely be unused.


Thanks..
November 22, 2007 5:38:29 PM

dengamle said:
4x1GB will run dual channel just as fine as 2x1024 + 2x512 will.

Dual channel and the lost ram is not related


What do you mean exactly, the dual channel an lost ram is not related. at first i wanted 4Gb moduals same speed /size in dual channel, know i understand the forth wont even be used, "wast of money" the third modual will run in single channel and only the "first two" will be in dual channel. honestly.. what benefit does dual channel really have over single channel. but if i were to go with the ram calculation you mentioned above, 2x1024 + 2x512 this would then give me 3Gb of ram "GREAT" thats all the ram i need, plus also know i now that thats all the ram my (windows XP 32b OS) can read anyway, still with the moduals in this configuration would thay still work in dual channel mode??
November 22, 2007 6:12:36 PM

It's a bit like RAID 0 where you stripe data across multiple harddrives.

In single channel the memory addresses are stacked, so 0-1GB would go to module 1, 1-2GB would go to module 2 etc.

In dual channel the addresses are ping-ponged between channels, so 0-1GB are spread across them all.

So you have full dual channel even though you cannot address the full 4GB RAM
November 22, 2007 6:58:22 PM

might just be worth buying 4 of the same DIMMS - might not be using a 64bit OS, but you never know.

I got both XP Pro 32/64 installed - xp64 reports 4gb ( vista ultimate x64 did too), xp32 reports 3.0GB.... ahh so it wastes a GB - nice having all DIMM sockets full of same DIMMS :pt1cable: 
November 23, 2007 12:36:41 AM

dengamle said:
It's a bit like RAID 0 where you stripe data across multiple harddrives.

In single channel the memory addresses are stacked, so 0-1GB would go to module 1, 1-2GB would go to module 2 etc.

In dual channel the addresses are ping-ponged between channels, so 0-1GB are spread across them all.

So you have full dual channel even though you cannot address the full 4GB RAM
The memory is not spread accross all the sticks only the two sticks that are in the same bank. It is my understanding that if the 4th stick is unusable, because the addresses are mapped to other components e.g., VGA etc., then it cannot be accessed, therefore there is no second channel in bank two.
November 23, 2007 4:58:45 AM

just to clarify, im going to be doing the same thing, atm i have 2x1gb ocz gold 667mhz, which is over a year old. looking at adding another 2gb of ram, but its going to be different as i can't find the same ram for a decent price. so the new stuff is going to be geil 2x1gb value select 667mhz ram. SO will this run in dual channel mode? or does it do like 2 sets of dual channel mode? or will it just go back to ol' skool single channel? O_o confusing much?
thanks for any help :-P
November 23, 2007 5:59:56 AM

If we look at the chipset the OP has...

915P http://www.intel.com/design/chipsets/datashts/301467.ht...

Section 12.2.1: Interleaved Mode

Addresses are ping-ponged between the channels, and the switch happens after each cache line (64 byte boundary). If two consecutive cache lines are requested, both may be retrieved simultaneously, since they are guaranteed to be on opposite channels.

Figure 12-1:

+------+ 4GB
| CH B |
+------+
| CH A |
+------+
| .... |
+------+
| CH B |
+------+
| CH A |
+------+ 0

You clearly see from the figure how the memory addresses are ping-ponged between channels. That means the lost ram is shared equally between them. So no matter how much ram is lost, you have dual channel all the way.
November 23, 2007 11:01:12 PM

So what your saying is that the 4th GB of address space is lost with 512MB on channel 1 of bank 2 and 512MB channel 2 of bank 2. That makes sense.
!