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niskel
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Joined: 17 Nov 2004
Posts: 457
Location: Fredericton, NB, Canada
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 Posted: Fri Mar 17, 2006 7:35 pm Post subject: nVidia card with an 'extra' 128MB of mystery memory |
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I did an 'lspci -v' just out of curiosity and noticed something rather strange: | Code: | 01:00.0 VGA compatible controller: nVidia Corporation NV43 [GeForce 6600/GeForce 6600 GT] (rev a2) (prog-if 00 [VGA])
Flags: bus master, 66MHz, medium devsel, latency 248, IRQ 209
Memory at fb000000 (32-bit, non-prefetchable) [size=16M]
Memory at e0000000 (32-bit, prefetchable) [size=256M]
Memory at fa000000 (32-bit, non-prefetchable) [size=16M]
[virtual] Expansion ROM at f9f00000 [disabled] [size=128K]
Capabilities: [60] Power Management version 2
Capabilities: [44] AGP version 3.0 |
This looks pretty normal in itself but my card, a BFG 6600GT, is advertised to have only 128MB of memory while lspci is reporting it to have 256MB. Am I just not understanding something or does my card really have 256MB of memory? |
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NeddySeagoon
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Joined: 05 Jul 2003
Posts: 54831
Location: 56N 3W
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| Posted: Fri Mar 17, 2006 8:32 pm Post subject: |
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niskel,
lspci has identified a memory range - thats not the same as saying that all the memory is there.
Look in /var/log/Xorg.0.log to see what X detected.
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Regards,
NeddySeagoon
Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail. |
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niskel
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Joined: 17 Nov 2004
Posts: 457
Location: Fredericton, NB, Canada
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| Posted: Fri Mar 17, 2006 9:06 pm Post subject: |
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| The X log reports 128MB as expected. So what exactly is this range that lspci is talking about? I am asuming this range includes the regular 128MB of expected memory but why have the extra 128MB or range. Couldn't this cause problems if something was trying to read or write to this range beyond the physical memory? (I suppose that is what the driver is suposed to take care of) |
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NeddySeagoon
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Joined: 05 Jul 2003
Posts: 54831
Location: 56N 3W
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| Posted: Sat Mar 18, 2006 11:09 am Post subject: |
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niskel,
Video card memory, however much you have is arranged to be mapped to start at 0xe0000000.
Normally, address decoding is incomplete, so if you have 128Mb, the same physical memory appears in this space twice, if you have 64Mb, it apears 4 times and so on. With 512Mb, it won't all fit at the same time and the memory must be paged into 256Mb (or smaller) parts by the driver.
This is much like in real mode, when only 64kb of the video memory can actually be addressed by the CPU.
Real mode is only used by Linux during the boot process.
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Regards,
NeddySeagoon
Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail. |
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