How exactly does RAM count work?

[Oduig]

Hi all,

Recently I've encountered ram issues on several computers running various versions of Windows. This makes me wonder how exactly things as Total Memory and Available Memory (Task manager) are calculated, and how the general way of handling memory works.

Let's assume I'm running Windows 7 64 bit on a fully functional system. I have a 4GB RAM installed, and my graphics card has 1GB memory. According to the system information in the NVidea configuration panel, 1.5GB of the system's ram is dedicated to the graphics card. (Question: Is there a way to change this? I find 2.5 GB rather large just for graphics processing, and seriously doubt all of it is used.)
I would expect things to be like this.
Total memory - Just under 5 GB. If I'm correct, the total memory includes the graphics card memory. Some 10MB is used for the bios, or system resources.
Available memory - 2.5GB, since 1.5GB goes to the graphics card and the rest is usable by windows/applications.


Now to reality. I'm running Vista 32 bit, with 4GB Ram installed and a graphics card with 1GB memory. An additional 1.5GB of the system's ram is dedicated to the graphics card. Since a 32 bit operating system can (by default, without tricks) address 4GB of total ram, I'd expect the following stats.
Total memory - just under 4GB. This is 3GB system ram and 1GB gfx card ram.
Available memory - 1.5GB. Yikes. This is since half of the 3GB is reserved for the graphics card.

However. The actual stats from my Vista 32 bit installation look like this.
Total memory - 3.5GB
Available memory - 2.7GB
System information reports 2.3 as available. (Why is this different from the task manager?)

My questions:
- Why does my graphics card need 2.5g dedicated ram?
- Why is the total memory not 4gb, and if windows doesn't inlcude gfx memory in the count, why is it not 3gb?
- Why is only 2.7 memory available?
- Why is, at the same time, only 2.3 memory available?
- What are the actual limitations on my system by using a 32 bit operating system.


I'm not looking for advice on how to improve my memory limit or which OS to use. I just want to understand. Thanks you for reading and helping me clear up this mystery.

 

[Nailezs]

i believe that some of your questions have to do with page file, and not ram. lemme find a thread that might answer some of your questions...1 sec

read
http://forums.techpowerup.com/showthread.php?t=91260
and see if it answers any of your questions
i've read that thread like 3 times, and while i understand that its just the way things work, i dont necessarily understand the why of it lol.

 

[Oduig]

That answers the question as to why my graphics card uses so much ram. Still, running dx10, I don't get why I have to miss out on 1.5gb ram just in case I want to run a game which copies gfx ram to my system ram.

Also, I don't see why page files use extra address space since the page files are located either on the RAM itself or on the HDD. I assume the HDD page files don't count towards the 4gb, otherwise using virtual memory would be counter-productive.

 

[Nailezs]

now those questions i cant answer lol. like i said, i dont know the why's, just the whats

 

[Oduig]

Sorry for answering my own questions, but I figured this may be informative for other people as well.

http://www.mydigitallife.info/2007/...-maximum-supported-ram-physical-memory-limit/
http://osdir.com/ml/suse.amd64/2005-07/msg00110.html

The above sites provide a plausible explanation as to why only 3.5 out of the addressable 4gb are used. A part of the memory (often 500mb) is reserved for PCI slots, even when there's no device inserted in the slot. By using memory remapping you can enhance the address space cause it makes the unused 'PCI memory' usable for other applications.

As for the 'available' memory, this seems to be the memory that is not only available for application use, but isn't put to use at that moment. This would explain the drop from 3.5GB to 2.7GB.

Remaining questions:
- Why does my graphics card need 1.5g of system ram, and is this ram a hard reserve or an upper limit of what the gfx card can use?
- What is the significance of the 2.3GB 'available' memory in System Information as opposed to the 2.7GB?
- As for 'what are the actual limitations', I suspect I would have 1GB more memory (4.5) if I had more address space, though I'd still like confirmation of this. Could someone with a 64 bit os and a 1gb vid card check that their 'Total Memory' is indeed larger than the combined size of their RAM?

 

[TheLaughingMan]

I have a 64-bit OS and 896 MB GTX card.

The break down of RAM "usage" is a little weird in Vista. A GTX in Vista does clone its memory into system RAM because of how the old WDDM works. As such, the GTX card will use RAM equal to its onboard GDDR RAM size. In your case that should be 1 GB.

The Vista RAM "usage" chart shows you total ram, used ram, and pre-allocated ram. The ram listed as "available" is pre--allocated to be used immediately. This is why their is a different between it and your total RAM as the remaining RAM will only be charged and ready if needed. This is done to cut down on power use, strain on the RAM chips, etc.

Not sure why it says your GTX card is using 1.5 GB

You would indeed have much more RAM if you had a 64-bit. The address space for a 64-bit OS is far far higher than 4 GB. YOU need to switch to a 64-bit OS. You should also switch to Windows 7 64-bit because they redesigned the WDDM to stop doing the clone in the system RAM, thus giving you even more of your RAM back.

32 bit Total Memory = (RAM - address space lose) + Paging Files
64 bit Total Memory = RAM + Paging Files

 

[ZenZimZaliben]

TheLaughingMan is dead on.

However you can fix this. http://support.microsoft.com/kb/929605

Add the /PAE switch to the boot.ini file, this will access the full 4GB, but will limit 2GB to the OS and 2GB to programs. If you add the /3GB switch after the /PAE it will allocate 1GB RAM to the OS and 3GB to all other apps.

You can free up more memory by switching to SSD's and turning off the pagefile...well I guess you could turn off page file regardless of HD type. It is recommend turning off pagefile with SSDs.

 

[CrackerJack]

Remaining questions:
- Why does my graphics card need 1.5g of system ram, and is this ram a hard reserve or an upper limit of what the gfx card can use?
- What is the significance of the 2.3GB 'available' memory in System Information as opposed to the 2.7GB?
- As for 'what are the actual limitations', I suspect I would have 1GB more memory (4.5) if I had more address space, though I'd still like confirmation of this. Could someone with a 64 bit os and a 1gb vid card check that their 'Total Memory' is indeed larger than the combined size of their RAM?

Reason why it's show 1.5gb is because of your AGP size setting on you motherboard. Most boards allow you to change this. If you can change this setting in the bios, then set it at 128mb or 256mb. I have this same issue. My board doesn't have AGP size controls so I have around 3gb of GPU RAM. Adding the PAE tricking mostly likely won't help you.

last question- Hope this helps
I have a 1gb gpu and 6gb ram on windows 7 x64. Windows will see total physical memory, not adding gpu or page file memory. CCC or Nvida reads the drivers for this type of info i believe. So it's not going show share memory. Same with GPU-Z. Windows usually will show both physical and shared memory.

Hope some of this help