4x CM2X1024-6400C4 in ASUS P5B Deluxe

[voidrunner]

I got the 2 sets of 'Corsair XMS2 TWIN2X2048-6400C4 Matched Pairs' (4x 1Gb CM2X1024-6400C4)
I have ASUS P5B Deluxe WiFi/AP motherboard

BIOS shows only 3008MB of RAM. Not 4000MB

Maybe I've read ASUS QVL wrong, but wasn't the board supposed to support all 4Gbs?

[Yellowbeard]

Find the memory remapping option in the bios and enable it.

[voidrunner]

Thanks
I changed the setting and now BIOS displays 4096MB (YaY)
However, windows (vista 32) displays 2gb in system properties
any idea whats up with that?

thanks again

[Yellowbeard]

I have seen users posting with that same issue but, I don't recall seeing a resolution. You may want to Google for it or contact Microsoft. What video card (or cards if Crossfire) do you have and how much onboard memory does it have?

[voidrunner]

I found an answer:
http blogs.msdn.com/hiltonl/archive/2007/04/13/the-3gb-not-4gb-ram-problem.aspx

Windows 32bit will not support more than 3gb
I gues my only option is to either lock it at 3gb or install 64bit windows

[Yellowbeard]

Windows 32bit will not support more than 3gb
I gues my only option is to either lock it at 3gb or install 64bit windows

This is not correct. It will support up to a maximum of 4096mb (4gb) of system memory. However, the onboard devices (such as video cards) detract from this amount.

What video card (or cards if Crossfire) do you have and how much onboard memory does it have?

[voidrunner]

I have X1950Pro with (i think) 512mb ram

[Yellowbeard]

Then, under ideal circumstances your system should see approximately 4096mb minus the video card memory, minus the CPU cache, and any other items with onboard memory (sound card, etc). So, you should see approximately 4096mb - 516mb = 3580mb "IF" Vista and your MOBO are playing nice.

[voidrunner]

weird.. im seeing 2047MB

[Yellowbeard]

That's the issue I was referring to. If you enable the memory remapping so the bios can see all 4gb, then the OS does not see it all. If you disable memory remapping, then the OS sees more memory. Try clearing the CMOS and then try it again with the memory remapping disabled and see what happens.

[Mossy]

For your operating system to see 4GB and over you will require a 64bit operating system, 64bit OS will be able to see 4GB and over "in" windows. On boot up your motherboard will only see 3.5GB as some of this is used for the PCI addressing values.

Hi Yellowbeard I hope you don't mind me in your forums (tell me if I am not) :-)

[Yellowbeard]

Hi Yellowbeard I hope you don't mind me in your forums (tell me if I am not) :-)

You are more than welcome here Paul, I'll take all the help I can get and appreciate you SCAN fellows!

What's odd to me is that if he allows the memory remap for the bios to see 4gb the OS can only see 2048mb. If he disables memory remap, then both the bios and the OS see only 3008mb of memory. By my math, both of these are incorrect even with a 32bit OS.

[Lucio]

Here's a thought, try disabling dual channel mode in the BIOS. It could be that the BIOS is being rather silly and saying "hmm, I've got more RAM here than I can properly address, I know, I'll assign addresses to this big block here but well, that other block, it's bigger than I can handle, I won't do it at all"

[Shooty*]

Can anyone tell me WHY the onboard devices detract? And when they do, is the memory you "lose"/ that the onboard devices "use" actually useful? Does stuff cache in there or something? Do they still eat into your ram if you have 2 or 3 gb? if not, why not?

I mean, if that "lost" ram is still helping performance, then fair play, but if not then why do the onboard devices use it at all?

[Yellowbeard]

First, you cannot disable dual channel in the bios. This is not an option and will not affect how much memory your system can address.

Here is a good link: http://en.wikipedia.org/wiki/32-bit

From the link:

In computer architecture, 32-bit integers, memory addresses, or other data units are those that are at most 32 bits (4 octets) wide. Also, 32-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. 32-bit is also a term given to a generation of computers in which 32-bit processors were the norm.

The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295 or −2,147,483,648 through 2,147,483,647 using two's complement encoding. Hence, a processor with 32-bit memory addresses can directly access 4 GiB of byte-addressable memory.

This example shows a physical limit of a 32 bit CPU. The same applies to a 32 bit OS and means that with a 32 bit OS your system can assign virtual address space for a TOTAL of 4gb of memory. Your system cannot disallow the onboard device memory as the devices with this memory must have access to it or they cannot function. So, of the 4gb total, the CPU cache, the video card memory, and any other devices with memory are given address space before the installed system memory. Since there is a cap at 4gb, if you have 4gb of installed system memory, there is no available address space for some of it. This amount subtracted from the 4gb total is dependent upon your hardware configuration.

Here is an easy example. Let's assume you have a normal system with 4gb (4096mb) of memory installed and are using Windows Vista, 32 bit. Your CPU has a 4mb cache and your video card has 92mb of memory and there are no other devices with memory that have been allocated address space. In this case, your OS would "see" 4000mb of memory available or, 4096- (92+4) = 4000mb. In this same example, if you have a video card with 512mb of memory, then your OS would see 4096 - (512 + 4) = 3580mb.

There is no magic to it. It is a limit of the OS. It applies to 32bit XP also.

[Lucio]

First, you cannot disable dual channel in the bios. This is not an option and will not affect how much memory your system can address.

Fair enough, I've seen that options in some BIOS's where you had the option. I understood why there's the cap and lesser amount seen, but it was an idea as to why it was seeing less than would be predicted.