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Re: 64 bit computers systems

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Jason Christensen wrote:

Sorry stated that wrong,


So if I install (2) dual core 2gb, equaling 4gb, will I be able to use 4.0gb or windows will only recognize ~3.5gb?






-----Original Message-----
From: Bill Allen [mailto:t.w.allen(--nospam--at)]
Sent: Monday, October 29, 2007 3:36 PM
To: seaint(--nospam--at)
Subject: RE: 64 bit computers systems


What’s the difference?


T. William (Bill) Allen, S.E.


Consulting Structural Engineers
V (949) 248-8588 F(949) 209-2509

-----Original Message-----
From: Jason Christensen [mailto:jason(--nospam--at)]
Sent: Monday, October 29, 2007 1:06 PM
To: seaint(--nospam--at)
Subject: RE: 64 bit computers systems


So if I install (2) dual core 2gb, equaling 4gb, I will only be able to use ~3.5gb or windows will only recognize 3.5gb?




You will be able to use ALL of the 4GB, but somewhere between a half-Gig and a full Gigabyte will be used for system housekeeping:

"The PCI memory addresses starting down from 4 GB are used for things like the BIOS, IO cards, networking, PCI hubs, bus bridges, PCI-Express, and video/graphics cards. The BIOS takes up about 512 KB starting from the very top address. Then each of the other items mentioned are allocated address ranges below the BIOS range. The largest block of addresses is allocated for today’s high performance graphics cards which need addresses for at least the amount of memory on the graphics card. The net result is that a high performance x86-based computer may allocate 512 MB to more than 1 GB for the PCI memory address range before any RAM (physical user memory) addresses are allocated."

(That's from the document I referenced earlier).

FWIW, this housekeeping will ALSO be needed with a full 64-bit OS, but since the address range is up to 32GB, it will be noticeably less.

But note: If you have 4GB of RAM in a 32-bit machine, or the same amount of RAM in a 64-bit machine, you're going to have the same amount of AVAILABLE physical memory. It's just that the 64-bit system will have VIRTUAL address space far beyond 4GB (however, I'm not sure if the system addresses can be located in Virtual Memory - I sort of doubt it).

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