Messages in this thread | | | Date | Wed, 2 Jun 2004 08:17:21 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | Re: Intel 875 Motherboard cant use 4GB of Memory. |
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On Tue, 1 Jun 2004 reg@dwf.com wrote:
> > > That could be PCI devices. Some (particularly high-end video cards) > > take up a lot of address space, which comes straight out of the available > > 4 GB physical address space. > > > > Check /proc/iomem. > > > > OK, that leaves me more confused, and (to me) it still looks like a > BIOS problem rather than a greedy device. Here is the /proc/iomem > with some decimal annotations: (as noted, there is 4x1GB of memory installed) >
Not just Intel motherboards. There is 32 bits of address-space. This needs to be shared between RAM and the I/O addresses of PCI/Bus and AGP boards. Unfortunately, the PCI/AGP specification wastes a lot of address space because something that needs 1 megabyte of address-space must sit on a 1 megabyte boundary. If this comes after something that used 128 bytes, there is nearly a megabyte wasted to get to the next boundary. A megabyte here a megabyte there.. pretty soon you are talking about a lot of wasted address-space.
Solution: A 64 bit machine will have the same problem, you end up wasting RAM address space if it overlays PCI/Bus space. But, you probably would never opt for a gazzzilion bytes of RAM anyway?
One gazzzilion = 1844 6744 0737 0955 1615 (2 ^ 64)
Just don't put 4 gigs of RAM in a 4 gig address-space and expect to use it all. Sell the spare 2 gigs or build another PC with it!
Cheers, Dick Johnson Penguin : Linux version 2.4.26 on an i686 machine (5570.56 BogoMips). Note 96.31% of all statistics are fiction.
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