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Need help with 3GB switch in XP Pro

Last response: in Memory
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May 21, 2009 1:16:45 PM

I have 4GB of memory in my system (2 2GB sticks) and XP is only recognizing 2.75GB. I added the /3GB switch to the boot.ini file but it still will not recognize any more than 2.75GB. Any other options to get this to work?

More about : 3gb switch pro

a b } Memory
May 21, 2009 4:57:41 PM

The /3gb switch does absolutely nothing to get you more address space. It merely re-allocates the 4GB that already exist from the default {2GB System + 2GB Application}, to {1GB System + 3GB Application}

Be WELL advised:

(1) If your system requires more than 1GB of address space in order to run, your computer *will* crash every time the allocated space has been exceeeded.

(2) Your Applications have to be written and flagged as Large_Address_Aware in order to take advantage of the space you've reallocatated. If not, you gain nothing.

(3) You have done exactly nothing to address the limitation of a 32 bit operating system. All you have accomplished is re-arranging what is there.
a b } Memory
May 21, 2009 4:58:24 PM

In a computer all bytes in the memory system need a unique name. This is called an address. For example, if you have 2 GB of main memory, then there are 2147483648 bytes of RAM in your machine, each of which require an address for the operating system to communicate to it. To give these all an address you need 31 bits to do it. Now, if/when you have 32 bits, you can name 4 GB (2 bytes to the 32nd power = 4GB).

This is why the total addressable space available in a 32 bit OS is 4GB – the OS runs out of addresses and cannot communicate/locate any more bytes of memory because of that.

You may think ”Hey, 4GB of address space… 4GB of RAM… What’s the problem” The problem is that memory isn’t the only thing needing an address. If you install a total of 4GB worth of RAM, the system will detect/use/display less than 4GB of total memory because of address space allocation for other critical functions, such as:

- System BIOS (including motherboard, add-on cards, etc..)
- Motherboards resources
- Memory mapped I/O
- Configuration for AGP/PCI-Ex/PCI
- Other memory allocations for PCI devices

Different onboard devices and different add-on cards (devices) will result of different total memory size. e.g. more PCI cards installed will require more memory resources, resulting of less memory free for other uses.

This limitation applies to most chipsets & Windows XP/Vista 32-bit version operating systems. Again, this is a limitation of the Operating System not having enough address space to allocate to the system *and* the RAM. Not allocating address space to devices renders them inoperable. Not allocating addresses to RAM simply results in the unaddressed section not being used in an otherwise fully functional computer. Therefore the OS designers assign RAM last.


If you install a Windows operating system, and if more than 3GB memory is required for your system, then the below conditions must be met:

1. A memory controller which supports memory swap functionality is used. The latest chipsets like Intel 975X, 955X, Nvidia NF4 SLI Intel Edition, Nvidia NF4 SLI X16, AMD K8 and newer architectures can support the memory swap function.

2. Installation of Windows XP Pro X64 Ed. (64-bit), Windows Vista 64, or other Operating System which can provide more than 4GB worth of address space.



Note: According to the latest Change Log published by Microsoft, Windows Vista 32bit SP1 will display the installed amount of RAM. This is a display change only.
May 21, 2009 5:50:28 PM

+1..... Scotteq...hit it on the head.....
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