Seeing only 379MB of 512MB DIMM installed [SOLVED]

helio · Apprentice Joined: 08 Apr 2006 Posts: 237

I have recently installed a 64-bit gentoo (amd64) on a very old HP Pavilion a736n Desktop PC. The system has a 512MB DIMM installed, but the OS seems only able to access 379MB of memory, as indicated by the free, top, and cat /proc/meminfo commands, even though the BIOS still shows 512MB of DIMM available. Is there anyway I can access the entire 512MB memory? Thanks.

NeddySeagoon · Posted: Mon Sep 20, 2010 8:12 pm Post subject:

helio,

At a guess, I would say that 128Mb of your RAM is being donated to on board graphics.
In your BIOS, see if you can reduce the RAM used for graphics. 32Mb will be plenty unless you have ambitions to run 3D with texture support.

I have not looked up the specifications for your machine but

helio · Apprentice Joined: 08 Apr 2006 Posts: 237

NeddySeagoon,

thanks for suggestion.

From the hp spec page, the graphic card is said to be "Integrated with up to 64 MB allocated video memory". But /var/log/Xorg.0.log says

(--) SIS(0): 131072K shared video RAM (UMA)
(--) SIS(0): DRAM type: DDR SDRAM
(--) SIS(0): Memory clock: 182.554 MHz
(--) SIS(0): DRAM bus width: 64 bit
(--) SIS(0): Linear framebuffer at 0xE0000000
(--) SIS(0): MMIO registers at 0xED000000 (size 64K)
(--) SIS(0): VideoRAM: 131072 KB
(II) SIS(0): Using 130496K of framebuffer memory at offset

So I am confused how much the video ram really is, or if the graphic card takes any system RAM as well?

drescherjm · Posted: Tue Sep 21, 2010 4:40 am Post subject:

The graphics card has no video ram so it takes system ram. And xorg and free are both telling you that it is taking 128MB of system ram.
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MotivatedTea · Posted: Tue Sep 21, 2010 4:40 am Post subject:

NeddySeagoon's probably got the right answer. Here are more details on how to go about testing it:

I'm not familiar with SIS graphics controllers, but on many lower-end or embedded graphics cards (especially Intel cards), the card itself has no video ram. It borrows memory from your system instead. You can often set how much memory is used in your BIOS. Start by checking there, and see if you can reduce the amount used as NeddySeagoon suggested.

If you can't find an option in your BIOS, or if it seems to have no effect, you might be able to control the value by using the VideoRam parameter in /etc/X11/xorg.conf. Assuming you're currently running without any xorg.conf file (as recommended), you should be able to create a minimal version that does nothing but change the VideoRam setting, something like this:

helio · Apprentice Joined: 08 Apr 2006 Posts: 237

Thanks everyone for the great suggestions.

Indeed the BIOS solution worked. The graphic card memory was set to 128MB by default for some reason, but 64MB and 32MB were the other two options. After I selected 32MB, now the top command indicates that 475264k system memory is accessible.