Before you buy 4Gb: Things you need to know

So many keep asking this question so please read this.

With the development of and production of DDR3 RAM we can find DDR2 RAM very cheap in the market place and so many are buying 4Gb of RAM and then finding that the cannot actually use it.

There are 3 questions you need to address before you go out and buy that RAM and potentially just be wasting your money, they following has been copied from 2 primary articles on this matter;

"1. What OS Edition have you installed?

a. 32-bit Windows is limited to a maximum of 4GB and cannot see any pages above 4GB.

b. 64-bit Windows can use between 8GB and 128GB depending on SKU.

2. What address range can your processor actually access?

a. Typically that’ll be 40-bit addressing today for x64 (Intel EM64T/AMD64), but older processors may be limited to 36-bit or even 32-bit

3. Can your system’s chipset map memory above 4GB?

a. Mobile chipsets on sale today cannot (but that may change with time)

b. Newer workstations (which use chipsets developed for single or multi-proc servers) usually can."

How to answer these questions:

For the first question right click (RC) on "My Computer">>>>Properties on the "General" we can see System, this is stating your current OS you really want a x64Bit Edition here (this equally applies to Vista, XP or any (Linux distro?)).

You can also DL and install EVEREST:

http://www.majorgeeks.com/download.php?det=4181

Open Computer>>>Summary in the left hand column and second entry will show Operating System.

For the 2nd Question using EVEREST expand Motherboard and click on CPUID.

First entry in Instruction set "MUST" state "64Bit x86 extension" with a tick and "supported".

The final question on Motherboard Chipsets can be answered by looking at the "System Summary" from earlier and assessing the "Motherboard Chipset". Some of those Chipsets that do support memory mapping above 4Gb;

"• The chipset must support at least 8 GB of address space. Chipsets that have this capability include the following:
• Intel 975X
• Intel P965
• Intel 955X on Socket 775
• Chipsets that support AMD processors that use socket F, socket 940, socket 939, or socket AM2. These chipsets include any AMD socket and CPU combination in which the memory controller resides in the CPU."

References:

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

http://support.microsoft.com/kb/929605/en-us

So please make sure you can answer all of these questions before buying that 4Gb of RAM and potentially wasting money.

 

very good explanation, this should be stickied

 

Interesting. I thought the limit was 3.5GB RAM for 32 bit Windows.

It's a poor day when nothing is learned.

 

It is 4Gb but both of the articles indicate that in a 32Bit OS, memory from the RAM is taken away by hardware devices. So that PCI-e Video Card "reserves" the 256Mb of memory it has from your RAM. Both of the articles discuss this in greater depth.

 

That makes sense.
Thank you for clearing that up.

 

Thank you lets hope an admin thinks the same.

Here is a list of the Intel Motherboard Chipsets that will support EM64T (therefore 64Bit OS and 4Gb and greater RAM):

http://www.intel.com/cd/channel/reseller/asmo-na/eng/203142.htm

Here is a list of AMD64 Motherboards (and I assume they will support any 64Bit OS):

http://www.freebsd.org/platforms/amd64/motherboards.html

 

Thanks for the info. Great post - very clear and concise explanation.