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Originally Posted by gosha
Does it mean I can install a amd64 version on a i386 machine? Is it any worth the effort? Would everything work just like with the i386 version?
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The Intel Core 2 Duo supports "Intel 64" which is Intel's reimplementation of AMD's 64-bit extension to the x86 architecture (Long Mode).
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Originally Posted by http://www.openbsd.org/amd64.html
OpenBSD/amd64 runs on AMD's Athlon-64 family of processors in 64-bit mode. It also runs on processors made by other manufacturers which have cloned the AMD64 extensions. (Some Intel processors lack support for important PAE NX bit, which means those machines will run without any W^X support -- it is thus safer to run those machines in i386 mode).
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As such, you
might notice some additional memory using the amd64 port.. but "bigmem" (>4GB) still isn't supported yet.
The 32-bit i386 (Protected Mode) can only access 32-bit's of address space.. 2^32 (2 to the power of 32) is == 4294967296 bytes (4GB).
RAM is not the only thing mapped into physical address space, other memory mapped devices reserve some of the valuable real-estate for their own purposes.. AGP aperture.. PCI memory ranges.. legacy ISA devices (serial, parallel, floppy, FPU, etc).
Enhancements were introduced to extend the physical address space, PAE and PSE36.. but the x86 is still fundamentally 32-bit by design.. registers and pointer sizes.. so some clever paging tricks are required to use more then that.
Even if OpenBSD/i386 supported PAE/PSE36.. you would still be limited to a theoretical maximum of 4GB of
virtual address space for user land processes, which is further limited by other architectural/OS limitations to 2GB of space.
It really is a complex and complicated subject, but unless you rely on and proprietary 32-bit only ports.. using OpenBSD/amd64 might just be beneficial in the long run.
Hope that helps.