4GB RAM installed, 3GB only visible on X60t, bandwidth issues

Hi all,

One of my biggest pet peeves with the X60t so far is the lack of a 64-bit processor option. Thankfully this looks like it's about to change, but I'm stuck with the 32-bit Core Duo, hence my problems.

I ordered mine with 2 x 1GB sticks of RAM, but I use Photoshop and Matlab with very large datasets, so I decided to try and upgrade it to 3-4GB (even though i know that each app can only use 2GB in a 32-bit environment). I have 8GB on my dual Opteron desktop running WinXP 64-bit, so I realize some of the issues with >3GB RAM.

Anyhow, to report my findings:
1) I first upgraded to 3GB RAM with 1x 2GB module and 1 x 1GB module. Windows saw 2.99GB (close enough). However, some people have mentioned that the Intel 945 chipset uses dual-channel RAM if the two modules installed are equal in size, so theoretically one would see a drop in bandwidth (5%?) if I had mismatched modules like this case.
More worrying, 3D performance would drop a lot more since video RAM is shared main RAM, and losing dual-channel bandwidth apparently impacts video performance more (do a Google search for this issue on MacBooks if you are interested, there was a lot of discussion about it).

Anyhow, when I tested memory bandwidth using Sandra, I indeed found a small drop in performance ranging between no change to about 2% or so slower. 2D and 3D performance dropped appreciably in certain tests using PerformanceTest 6.1, but stayed the same in others. The Simple 3D test showed a almost 18% drop when I moved from 2GB to 3GB. This is disturbing.

2) To get around this I managed to borrow another 2GB module and install it. Now I have a total of 4GB of ram, 2 x 2GB. All modules are 667Mhz (PC2-5300), so none of the speed issues are due to underclocked memory. This was also checked in Sandra which showed 667Mhz RAM.

However, Windows now only still sees 3GB!! I was expecting 3.5GB of RAM, due to the mapping of BIOS and video addresses into the top part of the 4GB address space, a well known issue in XP 32-bit. Pressing F1 to go into BIOS shows 4096MB of RAM installed, ok. however, if you turn on the full memory check option, upon startup it does the memory test which only goes to 3GB of extended RAM.

What gives? I'm feeling cheated out of my 0.5GB of RAM that I _should_ be able to see in Windows but am not. However, the ironic things is that memory bandwidth and 2D/3D performance are now back to the same levels as with the 2x 1GB modules, as dual-channel is now restored!

Anyone have any ideas how to get the remaning 0.5 or 1GB visible in Windows? There is no memory remapping option in the X60t BIOS, and PAE is on by default since DEP is on.

Thanks a lot, hope this helps others trying to upgrade to 3 or 4GB RAM.
Yeang

 

Well, found out more - the Macbook Pro uses the same chipset (I think), and people have found that there's the same 3GB limit.
The problem then becomes that you either lose dual-channel capability and some video performance, or have 1GB of RAM wasted doing nothing.

This is from Jason O'Grady's blog:

The MacBook Pro Core 2 Duo presumably uses Intel's 945PM chipset, which can physically handle 4 GB of DDR2 RAM. However, a number of items that must be stored in physical RAM space, and when RAM reaches 4 GB, there is some overlap. In other words, in a 3 GB RAM configuration, there is no overlap with the memory ranges required for certain system functions. Between 3 GB and 4 GB, however, system memory attempts to occupy space that is already assigned to these functions. For instance, the PCI Express RAM allocation occurs at somewhere around 3.5 GB of RAM and requires 256 MB of RAM. Thus, the virtual space between 3.5 GB of RAM and 3.75 GB of RAM is occupied by PCI Express data. So in a system with 3 GB of RAM, nothing is being wasted because the memory space required by PCI Express is still between 3.5 and 3.75 GB, and the installed system RAM does not violate this space.
The net result is that at least 3 GB of RAM should be fully accessible, while when 4 GB of RAM installed, ~700 MB of of the RAM is overlapping critical system functions, making it non-addressable by the system.

 

Actually, this is even more disturbing than I thought. I had assumed that the Core 2 Duo version of the X60t would get around this 3GB limitation due to its 64-bit capability. Reading what I just posted, I realized that same problem will still apply as it is a 945 chipset problem, not a CPU issue!

Anyone who gets the first Core 2 Duo, please upgrade to 4GB RAM and see if it's all visible in Vista 64-bit!

Yeang

 

I was under the impression that you needed the 965 chipset (Santa Rosa aka Centrino Pro) to fully take advantage of the 64 bit processors. Perhaps this is one of the things that will get addressed.

 

upgrade to vista and you'll get your 4GB...

 

Yes, after reading numerous posts on the thinkpads forum on this subject, you are correct that only the Santa Rosa chipset will get around this. Upgrading to Vista will NOT give you access to 4GB from what I have read - people have tried installing everything from Vista 64-bit to 64-bit Linux flavors and still have only seen 3GB.
Apparently it is a chipset limitation not an OS one.

 

Thanks, Ychng, for your post. I myself wanted to start a discussion on this yesterday when I was planning to buy a 2 sticks x 2GB = 4GB DDR2 PC2-5300 memory. I did a similar search and found what you essentially found, that the X60 Tablet, because it uses Intel 945 chipset, is limited by the 3 GB in Windows, even though the BIOS can see the 4GB. I tried to have Lenovo's Tech Dept address this who seemed to NOT know anything about this--I have yet to receive a reply from them.

What interests me more is NOT the issue of being "shortchanged" by what you see in Windows as the "missing" 1GB after installing a pair of dual-channel 2GB = 4GB. I want to know IF after installing the paired dual channel PC2-5300 667MHz 4GB memory (2GB x 2 sticks) AND running your power-hungry, large datasets data analytic and graphic tasks, if you indeed got a performance boost (and if so, by how much) as compared to the paired dual channel PC2-5300 667MHz 2GB memory (1GB x 2 sticks). In short, was there a performance boost in doing your extremely demanding computing tasks by installing the expensive 4GB (paired 2GB) versus the relatively inexpensive 2GB (paired 1GB)? Can you get away with just 2GB (paired 1GB) in doing your large data analytic/graphic tasks?

On a similar note, upon searching items on this issue yesterday, I stumbled upon Lenovo's technical pages that seemed to prefer a total of 3 GB by using one stick of 1GB PC2-5300 667MHz plus 1 stick of 2GB PC2-4200 533MHz, instead of a total of 4GB by using 2 sticks of 2GB PC2-5300 667MHz for the X60 Tablet PC. Any views, anyone, on this? Maybe, YCHNG, you can perform a 3-way test comparing 4GB (2 sticks of 2GB PC5300) vs 3GB (1 stick of 2GB PC4200 + 1 stick of 1GB PC5300) vs 2GB (2 sticks of 1GB PC5300) for your demanding large data/graphics tasks for our X60 Tablet running Vista. Note also that on Lenovo's website, if you want to configure a total of 4GB, they do NOT have an option for 2 sticks of 2GB PC2-5300 667MHz, but only 2 sticks of 2GB PC2-4200 533MHz. Can you also test this, and make a 4-way match-up?

Thanks again, all, especially YChng.

 

Strange isn't it, that Lenovo recommends a 2GB stick at 4200 speed? My guess is that they just have no access to 2GB sticks at 5300 speed. I would bet anything that installing any stick at 4200 speed will drag all RAM down to 4200 speed (533Mhz) even if the other stick is at 5300 (667Mhz).

I do not have access to 4200 speed RAM, so that is a test that I can't really perform. To answer your question, I have plenty of real world experience using Matlab and Photoshop on computers with anywhere from 1GB to 8GB of RAM, and the benefits are clear. HOWEVER, all the computers that had >2GB of RAM were running WinXP 64-bit where each process can take up more than 2GB of RAM. That's the caveat. I'm not sure how much improvement one would see going from 2GB to 3GB of visible RAM in WinXP 32-bit. I would think there would be benefits, as if say Photoshop took up its entire alloted 2GB space, there would still be 1GB left for OS stuff and caching etc.
In WinXp 64-bit however, Photoshop CS2 can use up to 6GB of RAM, so the benefits there are obvious, and quite discernible due to lack of swapping if you are working with a few 2GB PSB files.
With Matlab, it's not a performance benefit, it's more that with 32-bit matlab, the thing will just stop and give you an out-of-memory error if you try to process stuff that is too large. With 64-bit Windows and 64-bit matlab and 4GB RAM, i've yet to run into this (doesn't mean it won't happen).

I haven't used the 3GB configuration in 32-bit windows long enough to see if there is a big difference, so I can't really answer your question. Do i think it is worthwhile? Yes, especially if you are using Vista 32-bit which has the much-touted Superfetch technology to use every bit of free RAM to speed up your system.

Yeang

 

When I was ordering mine, I was checking the different RAM options, when I selected 4GB a little warning popped up saying "You have selected 4GB RAM, but your system only has capabilities for 3GB," or something like that. As far as why, I never bothered to look into it. I guess you could call up the Lenovo customer service people and ask. They might be having some issues with their site, and the thing didn't appear for you guys. It will be interesting to see why it can't use more than 3GB.

 

I hope this thread is still active. I too want to upgrade to 4gb for a performance boost. I read somewhere that if you upgrade to 4gb and map 1gb to video ram in the bios, then that's the best you can do.

Have you tried that? Does it give a performance increase over 2gb?