Fedora 64bit and Ubuntu 12.04 64bit sees only 7.8GiB when i have 8GB. no igp.
 

Hello, I recently using Ubuntu 12.04 64bit and i like it.

Windows and memtest86 both are saying i have 8155MB for full use. And windows say i have 8gb on computer properties.

Ubuntu says i have 7.8GiB in system monitor. I also booted Fedora 64bit live cd and it says the same thing.

Why?? As far as i can tell, there is nothing wrong with my memory.
I also use a dedicated GPU, so no igp is stealing my memory.

How much ram memory having you all in system monitor?
Does it also display less memory than in windows or memtest? Assuming you have no igp.

I am really worried since this is a new pc.


Thanks,

Member Response
 

Hi,

'1024 x 8 = 8192' this will be the total footprint (shift the 0 to increase the footprint i.e.10240 x 8= 81920. If you have shared video memory then that will be subtracted from the total memory. Even with video cards you will have some allocation for shared memory video processing, small portion depends on video card direct memory access control.

As to 'memtest86+' diagnostics, the program itself will take some space and do relocation once things are walking through so the whole footprint can be tested. 'memtest86+' does verify on memory sections to allow the program to overlay on pretested memory. Then relocate on validate memory again to test with varied patterns. 'memtest86+' does comprehensive pattern test on the whole footprint.

Your system does need kernel memory space and sometimes depending on modules or drivers the memory allocation will change. Growth for the kernel memory usage can vary over periods and loads.

Just remember that when speaking of memory you should use '1024' not '1000'.

Why the concerns? Experiencing memory issues? If using 'MS Windows as reference then take the 1024 factor when reading anything referenced by MS. MS does not present true memory foot prints unless you use proper tools to interpret.

Well, the strange thing is that i tested it with ubuntu 32bit and it says i have 7.9GiB vs 7.8GiB with 64bit.
How can this be explained?

Small correction, by default Memtest86+ does not test the whole memory. There is a small part of the memory (actually only a few MB) that is overlayed with the BIOS. These parts will not be tested. One can activate that in the options, but as the documentation states (and I have tested that to be true) you will errors that simply aren't there.

The 64 bit kernel simply has a larger footprint.

Member Response
 

Hi,

Your right, I omitted the 'BIOS' overlay.

Plus the 64bit Kernel seems to release more memory during init.

Really not a far comparison between Gnu/Linux as to memory allocations since each can be slightly different depending on kernel configurations.

That part that can´t be tested because it is overlayed with the bios, is that always in the same place of the ram? At every boot?
In that case, that ram part can be actually tested if you reverse the memory-modules on the motherboard.

A few years back that would have worked. Nowadays, with dual- and triple-channel memory controllers, which access the modules interleaved, this won't work anymore.

How is this possible? is it because, since it is interleaved, the date is ¨scattered¨ around the 2 dimms?

Exactly.

I just saw that my DDR3 DRAM Voltage is at auto setting 1.585V. The Asrock program reports the same voltage for the ram. However the ram modules are specified to work at 1.5V.
Is this a problem or is it oke?

Edit, i think it is better that this question has its one thread. So i made one.

So far as i understand:


8192mb is the total memory. Since bios overlay uses 37mb, the remaining memory is 8155mb.
ubuntu ¨should¨ showing 8155mb=7.96gb (like memtest) and windows.

But ubuntu 32bit is showing in hardinfo that i have:
8235888kb=8042mb=7.85GB. In system monitor it is rounded of to 7.9GiB

Ubuntu 64bit is showing in hardinfo that i have:
8141292kb=7950mb=7.76GB. In sytem monitor it is rounded of to 7.8

If i understand it correctly, Both ubuntu versions use a footprint which use a portion of the 8155mb memory and that portion of the memory is not shown. So Hardinfo shows the remaining usable memory, 8042mb/7.85gb for 32bit and 7950mb/7.76gb for the 64bit. Since the 64bit uses more memory for the footprint; thats why it shows less remaining usable memory than the 32bit version.
Hardinfo and system monitor do not show the footprint memory, only the 8155mb minus the footprint = Usable memory of 8141292kb=7950mb=7.76GB for the 64bit version of ubuntu.

To calculate how big the footprint is:
Since 8141292kb(64bit) = 7950.48046875mb
And the Memory minus the bios overlay= 8155MB.
8155MB - 7950.48046875mb= 204.51953125mb for the footprint.

Onebuck said:
So the kernel memory is stored in the same ram section as the programs memory? I mean in the usable 8141292kb/7950mb/7.76gb(64bit) remaining memory. There is actually 204.51953125mb more memory but that is used by the footprint. Or is the kernel memory the footprint? What is the footprint?

Other understanding:
Or can the total usable memory ubuntu is showing in hardinfo vary? From 8141292kb/7950mb/7.76gb(64bit) to xxxx? That is if the kernel memory is the footprint, if the size of the kernel memory changes so wil be the footprint because they are the same. Result: if the memory size of the footprint/kernel can change, so wil the total usable memory change.
But i don´t think the kernel is the footprint. Am i right?



I am a complete noob at this, but i am trying to understand.
It is actually quite interesting.

Oh, and really, really thanks for all the answers!