T400 Switchable GPU eating RAM

FYI, new T400 with discrete graphics and ordered with 3G RAM will show 3.0G available in bios and in System Information, but Vista will only see ~2.519G available. The culprit is the switchable GPU card which will allow you to flip between a dedidacted GPU when you are on grid power, and an integrated GPU when on battery. The battery savings is significant but I felt the memory cost was significant so I figured out how to disable this option and force the GPU to always be in dedicated mode and regain use of the full 3.0 G RAM.

If you choose to do this also, boot into bios and locate the Display options. There are two options that need to be set - one selects Integrated vs. Dedicated vs. Switchable, and the other enables the discovery of Switchable - which must be disabled to force the system to boot into any mode other than Switchable.

The battery will take a bit of a hit when running on battery, but the system runs noticable faster and full 3.0G RAM now available to Vista.

This was discovered when I ordered a T400 with the intent of giving my T61 to an office mate, and when the machine arrived the performance seemed slightly slower than the T61 and the memory showed missing ~512M, despite the system being loaded with a faster processor and faster memory and faster dedicated GPU card.

Once I disabled the onboard integrated graphics option, the T400 screams and is probably the finest laptop I've ever owned.

 

Don't know where you're getting Vista detecting less than your RAM because of switchable graphics. I've got 4GB and Vista detects it all with switchable graphics enabled.

 

I'm not so sure. My T61 have integrated graphics and it's even faster than my T42p with full dedicated 128MB on video. It could be a glitch on some driver that control the switching features, don't know for certain.

 

I am running Vista 32 bit with integrated graphics on my T400 and I see full 4.00 GB RAM

 

Running Vista 64 bit here with integrated graphics on my T400 and I'm able to see the full 4.0 GB RAM.

 

Just let you know, I also have a T400. I added 2 additional GB to take it to a total of 4 gb. I am only getting 2.5 in Vista Home Premium 32 bit. I have done research and came to the conclusion it would be all I would get, without a 64 bit operating system. I agree, it is a result of the hybrid graphics. Even after making the adjustments in the bios, I still couldn't get any additional memory available. I like the dual graphics anyway and I seem to have sufficient memory for what I am using the laptop. As a side note, the extra memory did increase my Windows Experience from 5.7 to 5.9 on memory. Best laptop, I have ever had and I have have many Thinkpads before this.

 

If anyone out there has a T400 with the ATI 3400 Series Switchable GPU and 3.0G if installed physical memory and running Vista 32, please try the following and post your results:

1) Change bios to NOT detect Switchable Graphics, and select Dedicated Graphics option. Save settings and reboot when leaving bios. Immediately do a complete power off and a power on reboot. How much memory does Vista report as available?

2) Change bios to detect Switchable Graphics, and select Switchable Graphics option. Save settings and reboot when leaving bios. Immediately do a complete power off and a power on reboot. How much memory does Vista report as available?

I'm getting 3049 available following option 1 above, and 2159 available following option 2.

Something is taking memory away when switchable graphics is enabled, and Lenovo support has indicated I should see entire 3G in both scenarios.

Thanks in advance if anyone has the time and configuration to do this test.

 

Me thinks this is some sort of hardware bug. It sounds like a memory addressing error, where the graphics memory of both video cards eat into the available memory addressing space (If there was to be a memory "eating" problem at all, it should occur when the graphics card with non-shared memory is active and not the other way around.).

My guess is that when you enable the integrated graphics card, the dedicated graphics card is still not completely "disabled" and its memory eats into the available 32-bit memory addressing space. However, if you run a 64bit operating system, your memory addressing space increases far beyond 4GB, thus alleviating the problem.

Hopefully, this can be fixed with a BIOS update.

 

Thanks for the feedback.

Current system bios shows v1.13, and the latest available download available from the lenovo downloads site is v1.12.

Not necessarily comfortable doing a downlevel bios update.

Also, correction on my previous post - I meant to say 2519G, not 2159G. It's consistent no matter how many times I enable/disable the switchable GPU.

 

On 32-bit operating systems -- memory mapped I/O is used to push data effiecently to and from devices.

Unfortunately the I/O mapping uses the same limited 2^32 address space as your computers main memory. The more devices which use it (And video cards use a TON) the less address space avaliable for real memory.

The best solution is to get a 64-bit OS since then the avaliable address space might as well be unlimited.

You can actually see these I/O mappings via the 'System Information' tool in vista. Click Hardware Resources / Memory. Might be able to turn off/disable hardware components your not using in the bios..irda,fireware..etc to reclaim some memory but I doubt you will be seeing any 'updates' to correct this.

 

So when I force the bios to use the dedicated GPU (which comes with 256M dedicated RAM), it uses the RAM it came with and does not impose on the system RAM?

And when I allow the bios to detect the switchable graphics, the integrated portion of the GPU reserves memory from system RAM?

That would explain why the T61 with solely dedicated GPU did not use any RAM and showed the entire 3G available.

Maybe I'll brave the scratch install to 64.

Anyone done this with a T400? And will 3G be sufficient for Vista Business 64?

 

This is also my problem.

At first my T400 had 1GB RAM, last week I upgraded the memory to 3GB, however Windows Task Manager only recognized 2519MB of total physical memory.

After performing some searches in the Internet, I found that there are some people also have this problem, meanwhile others do not. This strange. So, is there any solution to this?

And yes, I just followed this instruction...

...and the total memory is now 3049MB

But it means that I have to sacrifice the switchable graphic. So, power T400 users, please help me, how to solve this problem?

 

Same here. I have always had Latitudes and in November made the jump to a T400. Won't come out of sleep mode, memory issues, and the right front of the case is very flexible with a popping sound. Bought a MacBook last week and have been very impressed with my first Mac.

 

I have the T500 with 4Gb memory. When a 32 bit OS is installed it only shows 2.5Gb of RAM. With 64 bit OS I can use full 4 Gb. As described previosly this is because the computer has to map display memory to addresses and this can take up from your total memory (although that remaining physical memory is not actually lost or used).

Reading the posts above I think that the T400 has the same "limitation". If you use both display adapters then you cannot have more than 2.5Gb available because of the address space being used. Normally this issue would affect 32bit OS users with 4Gb of RAM (and they would see about 3.5Gb) but in this switchable case for some reason the system needs 1.5Gb address space.

If you think about it: two adapters == at least twice the address space needed.

So if this is correct it would not matter if you put in 2.8, 3, 3.5, 4 Gb of RAM into the machine, it would always use only a maximum of 2.5Gb of RAM (under a 32bit OS) because the rest of the address space is used up by mapping the video memory.

So when you disable one of the display adapters you get more RAM because less things have to be mapped. This is not a problem or not in the "this is a bug" sense of way - this is how computers work.

One solution is the one described above: disable one of the display adapters by going dedicated only. That will enable you to use 3Gb of RAM at least (probably more if you had 4Gb physical memory available, although not the whole 4Gb under 32bit).

While I realize it is not an option for everyone a better solution is to go 64bit. In that case you would see the memory available equal the installed physical memory. I myself have no problem running on 64 bit Vista, everything works like a charm.

 

So if you only run 2 GB of ram is it still going to take a significant amount?

Also, does any of this apply to the W500...i thought i read that it doesn't have the switchable option, so if that is right, do you you just have to deal with it. (sorry about the slight divergence off topic.)

 

No it doesn't apply when you have only 2Gb of RAM. You will be able to use all 2Gb of it - except if your gfx card uses system memory, like many integrated cards do. But that is a different case and does not relate to the problem here.

I am sure this has been explained in many places already, but here it goes again Mind you, this is very simplified.

Computers use addresses to specify a location in memory (a byte). In 32 bit computers the computer can use addresses that are stored as 32 bit numbers. This is sufficient to have about 4 billion addresses, which translates to about 4Gb of address space. The computer can use this address space (in a 32bit operating system) to address:

1. phsyical system memory (RAM)
2. operating system services and devices that require a region of addresses to access its functions

To stick with our case of graphics card, if your graphics card has 256Mb of memory the system somehow needs to access it. In this case (again, simplified) it will allocate 256Mb of addresses from the entire address space that refer not to your RAM but rather to the video memory on the card. When the computer sees and address that is in this region of the address space it will know to access the video memory on the graphics card.

Not just graphics cards allocate addresses this way but also other devices and the operating system itself. Also, the graphics card might allocate more addresses than there is actual video memory on the card - who knows what it needs it for?

So say the operating system and devices excluding gfx needs about 300Mb of address space (not RAM!) for itself. The ATI card wants, say, 600Mb and the Intel graphics card another 600Mb (these are just examples, I have not checked how much address space is needed). Now these amounts are not actual RAM (they might be in the end, but currently they are just numbers from the address spaces). This means that about 1500Mb of address space is needed to address these kinds of devices and services.

We are left with 2500Mb of address space (about 2.5 billion addresses) that the computer can use to address actual physical memory. If you have 2Gb installed, no problem: there will be 500Mb (so about 500 million) addresses that are not even used at all. If you have 3Gb however you have the problem where you have about 3 billion bytes of memory but only about 2.5 billion addresses to allocate to them. Clearly, you cannot assign an address to every byte of memory - hence the result: not all of your actual RAM is available to the system.

In the 64bit operating system you have much larger numbers to represent an address, so the address space is larger. There is no problem allocating 2/3/4 or even 8 billion addresses to the phsyical memory. Also, when you disable one of the graphics cards: the one you disable will not require addresses from the available address space. This means there are more addresses available to address the RAM.

 

In conclusion, the switchable graphic function eats memory because of 32bit windows! not a hardware or firmware problem, but a software problem!

only solution upgrade to 64bit OS or sacrifice switchable

 

Hello, first post for me on this forum...
I understand the limitation of 3Gb for Vista 32bit.
I also understands on-board video (Intel) eats RAM and a dedicated ATI should use it's own RAM.
I "accept" the "switchable mode" eats the RAM anyway for the Intel mode, and does not relase the RAM when switching to ATI mode dynamically via the Power Manager menu. (I would appreciate if the system could handle this RAM release)

What puzzles me is the RAM available when toggling modes in the BIOS.
I have a T400 with 2x2Gb physical.

When I set "Integrated Graphics" in the BIOS, Vista 32 SP1 starts with the Intel only video, but sometimes I have Task Manager reporting 2517 MB or 3029MB.
Similar, I had Vista reporting 2553 MB or 3065 MB while the BIOS was set to "Discrete".
This happens when I toggle the BIOS Video between Integrated and Discrete.

Not a very stable behaviour...
Unless it is Vista that is not reliable in reporting the available RAM ...

Am I missing something ?

 

Yes, there is one additional quirk to this story -- so far not mentioned in this thread.

First a repeat for any new readers: you see the memory Vista recognises in control panel -- system, the memory that it can actually use in task manager (ctrl-alt-del) -- performance tab. So for Vista 32 with 4GB RAM and switchable graphics the control panel will report 4GB and the task manager 2.5GB.

Now if you are willing to sacrifice switchable graphics and only switch manually in BIOS between discrete and integrated (ie like you have to do in XP where there is no switchable graphics) you can get an additional 0.5GB with task manager reporting 3GB if you have 4GB installed. Note that if you have 3GB installed you will never get more than 2.5GB in task manager -- I am not sure why.

However to get the 3GB instead of the 2.5GB you need to do the following:

Reboot and in BIOS change from switchable graphics to discrete graphics and also turn off the OS auto detect of switchable graphics

Boot and let Vista install the new driver in the discrete environment

Reboot again and go to BIOS and change from discrete to integrated graphics

Boot and let Vista install the new driver for the integrated environment

Reboot setting bios to whichever environment you want to use

After this third reboot when Vista has installed new drivers in both environments the task manager should now show 3GB instead of 2.5.

In other words switchable graphics doesnt let go until you have installed new drivers in both environments.

As I am using a modded ATI Catalyst 9.1 driver I have been running like this for 2 months now -- and task manager consistently reports 3GB.

 

Just get Vista x64 and you'll get to use all of your memory, while keeping the switchable graphics.

 

Right now its not an issue for me as I can't use Lenovo's old Catalyst 8.8 based switchable graphics driver anyway.

If we had got a working switchable graphics driver at the beginning of the year I probably would have gone to Vista 64 by now but as Lenovo still hasn't shipped a useable driver I am thinking about delaying and going directly from Vista 32 to Windows7 64.