-=PCTechTalk=- the issue with 32-bit operating systems and 4GB of RAM
- From: Gman <gman.pctt@xxxxxxxxx>
- To: "PCTechTalk Group <FreeLists>" <PCTechTalk@xxxxxxxxxxxxx>
- Date: Thu, 5 Feb 2009 16:28:41 -0500
This is the most clear & concise explanation I have ever seen on why 32-bit
operating systems cannot see 4GB of installed RAM. This was found within
the OCZ forums at the following link.
http://www.ocztechnologyforum.com/forum/showthread.php?t=28542
******************************
Windows XP w/SP2 or Vista will not recognize 4GB of ram when you are in
Windows.
The Windows OS (Vista and XP) can only address 2^32 bits (4,294,967,295) of
memory-mapped I/O (MMIO, henceforth). Everything in your computer has an
MMIO address; the BIOS, the buses, Video Card RAM (Which supersedes your
DRAM addressing). The computer reserves blocks of MMIO addresses for Video
RAM, then buses, bridges, BIOS, then DRAM. Your RAM gets all the addressing
space left, which is usually 2.5 - 3.25GB.
This means that you will not have 4GB available in Windows, it will show 2.5
to 3.25GB. The actual number will depend on your motherboard/chipset and
what other devices that require an MMIO address, are installed in your
machine. Remember that onboard sound, USB, SATA, all require MMIO addresses,
not just PCI or PCI-e cards. Basically the more things you use, the less
total ram you will have available.
64-bit versions of XP and Vista will see and use all 4GB since they have
more physical addresses available (2^64)
******************************
Peace,
Gman
"The only dumb questions are the ones we fail to ask"
http://www.bornagainamerican.org
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