Dual Channel memory with 3GB RAM

[fuxxociety]

I just bought a new laptop.. Toshiba X205-sli4

I had a rather lengthy discussion with the helpless desk, and ended up right where I started.

The older version of this laptop was equiped with the T7500 Memrom C2D processor, and 2x1GB matched pair of DDR - just fine for dual channel.

The newer version (that i bought) has the T8100 penryn core, with 3GB of DDR2 (1x2GB + 1x1GB)

While I understand that a 32 bit OS can only "see" 3GB of DDR, how does that affect dual channel mode? I was under the impression that dual channel could only function with matched pairs of the same type memory (like mirrored RAID)


Am I correct in this assumption? Should I pull the 2GB and throw 2x1GB in this machine?

 

[Foxery]

Dual channel simply means that if you have four RAM slots, 1+2 go to one channel, and 3+4 go to the other, regardless of how many slots have RAM actually plugged in.

 

[n7]

http://www.intel.com/support/m...sktop/sb/cs-011965.htm

 

[fuxxociety]

Rules to Enable Dual Channel Mode
To achieve Dual Channel mode, the following conditions must be met:

* Matched DIMM configuration in each channel
* Same Density (128MB, 256MB, 512MB, etc.)
* Matched in both Channel A and Channel B memory channels
* Populate symmetrical memory slots (Slot 0 or Slot 1)

Note: Configurations that do not match the above conditions will revert to Single Channel mode.

The following conditions do not need to be met:

* Same brand
* Same timing specifications
* Same DDR speed

So...

I've only got 2 slots in my laptop. One populated with a 2GB module, and one with a 1GB module.

According to that page, I'm NOT running in Dual Channel mode.

 

[cmdrmoocow]

Originally posted by: fuxxociety
According to that page, I'm NOT running in Dual Channel mode.

Correct.
However, if you're running one of the chipsets listed, it may be in Dual Channel Asymmetric mode. This allows fast access to your first two gigs and single-channel bandwidth to the last gig.

 

[pallejr]

Does your bios say you're in "flex" mode? Then you're running in the best possible mode with your config, dual from 0-2 GB and single from 2-3

 

[imported_wired247]

the odds that you are running programs all the time where you will significantly benefit from dual channel over non-dual channel are pretty slim, from some of the benchmarks I've seen.

 

[fuxxociety]

This is a Toshiba laptop, there is nothing in the BIOS or POST that tells me what mode my memory is running in.

If I were to buy another 2GB module, and run 2x2GB, would that work as expected on a 32 bit system in dual channel mode? (will the OS only see two gigs, or the entire array?)

I play World of Warcraft / Crysis / Final Fantasy XI on this laptop, I would consider the constant loading of textures, etc, in and out of memory to be a pretty significant need for dual channel.

Please, correct me if I'm wrong though.

 

[Nothinman]

If I were to buy another 2GB module, and run 2x2GB, would that work as expected on a 32 bit system in dual channel mode? (will the OS only see two gigs, or the entire array?)

32-bit Windows will only see 4G minus however much address space is stolen by hardware. You might get 3.9G and you might get 2G, it all depends on your hardware config. The only real limit is 4G and that's only because MS decided to impose that limitation on their 32-bit OSes.