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post #21 of 22
I'm glad i'm one of those oddlings that adopted 64-bit builds when DDR was still the standard..
Its nice to think "bah, I need more RAM"
and then hear the Corsair Rep whisper "You can have it"
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Jesus PC v5.3
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post #22 of 22
Quote:
Originally Posted by Coolwaters View Post
i will soon. probably when my friend gets his build i'll give him my vista.

can i fully use 8g with 64bit?
Maybe.

It gets a little complicated, so I'll do my best to explain why and people please correct me (with proof) if I say something wrong.

This is all rooted in 32-bit operating systems. 32-bit operating systems can only recognize a little more than 4GB of memory (2^32 = 4,294,967,296 or ~4.295GB). However, much of the last GB of memory is reserved for different hardware, such as your video card(s), to dump their I/O. This dumping ground is known as MMIO (memory mapped input output) proof and is often called a "memory hole". Google it and I'm sure you'll find a wealth of information. Basically what MMIO does is it reserves space in the memory address for certain devices to use. Think of it as reserving the space for a particular device, so it doesn't have to worry about other devices using it's memory lines.

So since a 32-bit OS can only deal with a total of around 4GB of memory, installing an 8800GT with 512MB of memory on the graphics card will only leave you with around 3.5GB of system memory to use. More space is reserved for other hardware and for backwards compatibility with older operating systems and devices, so you'll have even less than 3.5GB of system memory available. Windows says that the typical 32-bit Vista will be capped at 3.12GB of system memory available for use by the operating system, as the rest of the 3rd-4th GB is reserved for MMIO proof. The Vista service pack 1 will report all 4GB of memory, but you still can only use 3.12GB or so. They did this to shut people up because the average user doesn't actually care about the performance as much as the satisfaction of knowing they have 4GB of memory.

So how does this effect Vista 64-bit? Simple, backwards compatibility. The easiest way to deal with this memory hole was to leave it, pure and simple. This way there's no backwards compatibility issues, and actually you should be happy that they left it or Vista 64-bit would be complete trash. So on a typical system using 8GB of system memory and Vista 64-bit, you'll have about 7GB of usable system memory, because most of the space between the 3rd and 4th GB is reserved for MMIO.

But my answer was maybe, not no. So here's the catch, some motherboards support memory hole remapping. Basically this takes the MMIO and remaps it to a point so far out of reach by our current hardware that you never have to worry about it interfering with your system RAM. If your motherboard has this feature in the BIOS (it may not) then give it a shot. If it doesn't, big deal, you still have 7GB of memory which is way more than you need, at least right now in summer 2008. Memory hole remapping is rumored to be highly unstable, crashing the system if the space between the 3rd and 4th GB is accessed. But perhaps technology has improved recently and it works better now, I can't speak from experience on this. If you have it, give it a shot, but don't expect it to work.
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White Whale
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250GB Samsung Evo Noctua NH-D14 Windows 7 Professional 64-bit 24" Samsung ToC T240 1920x1200 
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Saitek Eclipse (Blue LED) 660W Seasonic Platinum SS-660XP Corsair 600T (white) OCZ Equalizer 
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XTrac Ripper 17" x 12" 
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