Maximum amount of RAM on a 64 bit OS?

binary_pearl · 08-23-2009, 01:16 AM

I was looking to upgrade the amount of RAM in my computer (currently 2GB), and was using `dmidecode` to see how many slots I have available. In my search I noticed that it appears that the Maximum Capacity is 4GB on my motherboard.

Even though I am running a 64 bit OS, is it correct to say that my memory controller will still only support up to 4GB of RAM? If there is any other information I can provide, please let me know, thanks!

--Shaun

sabayonnavi ~ # dmidecode -t memory | grep "Total Memory Size"
Maximum Total Memory Size: 4096 MB
sabayonnavi ~ # dmidecode -t memory | grep "Maximum Capacity"
Maximum Capacity: 4 GB
sabayonnavi ~ #

anon099 · 08-23-2009, 01:59 AM

yes. unfortunately and realistically, high levels of ram require more checks and balances(hence ecc). i have a 64bit processor and my motherboard will only support 16GB but only one brand of ram will be able to pull off 12GB. if you want to use a lot of ram you really need a server motherboard with ecc. there is a a reason that people pay twice as much for the same amount of memory(ecc).

Quakeboy02 · 08-23-2009, 02:18 AM

I've got 4GB in my machine, too, but I don't think I've ever seen usage above 1GB. If you're doing video editing or something like that, then you might get some benefit from it. Otherwise, if you aren't having swapping problems, then you won't see any benefit from upgrading. It's pretty common for the memory controller to be the limiting factor for memory.

johnsfine · 08-23-2009, 08:17 AM

Quote:

Originally Posted by binary_pearl

I was looking to upgrade the amount of RAM in my computer (currently 2GB), and was using `dmidecode` to see how many slots I have available. In my search I noticed that it appears that the Maximum Capacity is 4GB on my motherboard.

A lot of motherboards that claim a maximum capacity of 4GB really have a lower maximum capacity, 3 point something or even 2 point something GB.

You might want to research the motherboard further to find out how much ram you would be able to use if you installed 4GB.

Quote:

Even though I am running a 64 bit OS, is it correct to say that my memory controller will still only support up to 4GB of RAM?

If the memory controller only supports 4GB of actual ram (unlikely) then that limits you to 4GB. Nothing the 64 bit OS could do would get around that.

If the memory controller only supports 4GB of physical address space (more likely), that limits you to much less than 4GB of usable ram.

GrapefruiTgirl · 08-23-2009, 09:00 AM

Something else worth noting, which I'm not yet sure what to make of in my own case:

The DMI decoded information for my board shows:

Code:

Handle 0x0008, DMI type 5, 24 bytes
Memory Controller Information      
        Error Detecting Method: 64-bit ECC
<---snip--->
        Maximum Memory Module Size: 1024 MB     
        Maximum Total Memory Size: 4096 MB      
<---snip--->          
        Associated Memory Slots: 4              
<---snip--->
        Socket Designation: DIMM1  
        Installed Size: 1024 MB (Double-bank Connection)
        Enabled Size: 1024 MB (Double-bank Connection)  
<---snip--->
        Socket Designation: DIMM3  
        Installed Size: 1024 MB (Double-bank Connection)
        Enabled Size: 1024 MB (Double-bank Connection)  
<---snip--->
        Socket Designation: DIMM2           
        Installed Size: 1024 MB (Double-bank Connection)
        Enabled Size: 1024 MB (Double-bank Connection)  
<---snip--->
        Socket Designation: DIMM4  
        Installed Size: 1024 MB (Double-bank Connection)
        Enabled Size: 1024 MB (Double-bank Connection)

So based on the above, the memory controller supports 4096Mib (4-Gib) -- and in both 32 bit Slackware (w/PAE 64Gib enabled), and 64 bit Slackware, I have no troubles seeing/identifying/using all 4-Gib.

But, further down the DMI information, I see this:

Code:

Physical Memory Array               
        Location: System Board Or Motherboard
        Use: System Memory                   
        Error Correction Type: None          
        Maximum Capacity: 16 GB              
        Error Information Handle: Not Provided
        Number Of Devices: 4

Which leads me to believe that 16 Gib are supported (4x 2-Gib sticks, as there are 4 slots)

Now, below is from the manufacturers website/specifications for the board:

Code:

DIMM Slots  	4
Max Memory (GB) 	8

Which indicates 8 Gib supported!

So taken all together, I don't know what to make of it

as the information seems conflicting to me, and I'm not knowledgeable enough to make an educated guess..

The moral: DMI information is known to be inaccurate; whom to believe?

Sasha

pixellany · 08-23-2009, 09:22 AM

The title of the thread is about memory supported by the OS.

There are three things that affect how much memory can be used:
The cpu
The mainboard design, including chipset
The OS

If you have a 64-bit CPU and OS, then the limitation will be the mainboard. This would be the typical situation.

A 64-bit cpu and OS will support ~ 2^64 bytes of RAM = 1.84E19 (18.4 exabytes) How many 2GB sticks is that?......

GrapefruiTgirl · 08-23-2009, 09:31 AM

PS - sorry if my above post skirted the exact topic/OP question-- hopefully it added a teensy bit of value to the thread nonetheless..

Pixellany appears to have answered the exact question specifically.

Sasha

binary_pearl · 08-23-2009, 10:08 AM

Thanks all!

I am definitely swapping, but that's running compiz, firefox, and amarok, on a dual headed display. So I'm asking for my system to swap

This is good information, as at work I help maintain a very large number of linux x86 servers from different generations (from dual socket PIII's, to dual socket quad core's). We are trying to figure out how to spec out how much ram each server model can hold, and I think it's better to get the information from `dmidecode` vs the information from a salesperson

--Shaun

GrapefruiTgirl · 08-23-2009, 10:20 AM

FWIW, I too would probably trust DMIdecode farther than 'a salesperson' -- but do keep in mind, dmi information is not necessarily complete, nor necessarily accurate, a good part of the time..

Cheers,
Sasha