Date: Wed, 17 Feb 2010 16:52:00 -0800 From: Chuck Swiger <cswiger@mac.com> To: yuri@rawbw.com Cc: FreeBSD - <freebsd-questions@freebsd.org> Subject: Re: Is it possible to see memory over 3GB on 32-bit FreeBSD? Message-ID: <9D22BE72-E860-44D9-A582-86CE36AB6CBA@mac.com> In-Reply-To: <4B7C82F5.7030207@rawbw.com> References: <4B7C493B.1060503@rawbw.com> <20100217150217.393724ed.wmoran@potentialtech.com> <20100217202327.GA23365@owl.midgard.homeip.net> <4B7C82F5.7030207@rawbw.com>
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Hi-- On Feb 17, 2010, at 3:59 PM, Yuri wrote: > Erik Trulsson wrote: >> It very much depends on what hardware you have in the system. Just >> about every expansion card or I/O device will reserve some of the >> address space for its own use. Some devices will need a lot of space - a graphics card with 256MB of RAM on it will use (at least) 256MB of the address space for example. > > This doesn't seem like a good idea that video memory is always mapped to system memory. What if one day graphics card gets 4GB RAM? Then we won't even be able to have 32-bit OS working with such card and in 64-bit OS 4GB of memory would be grossly wasted. At one point, there was a considerable advantage to have video card memory fully mapped into untranslated address space so that various things could read or write as they pleased (cf "VESA linear framebuffer"); generally they gained speed advantages from this. With AGP's GART, the amount of memory available for textures, bump-maps, etc, could reside in video card memory, local RAM, or a combination. Modern video cards do not have keep their entire memory space mapped into address space; for example, a nVidia 275 card with 1792 MB of RAM doesn't seem to want more than 256MB of address space under 32-bit Windows platforms. Regards, -- -Chuck
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