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Dell Optiplex 745 with 4GB of RAM; Win XP Pro only sees 3GB.

I have a Dell Optiplex 745 with 4GB of RAM; Win XP Pro only sees 3GB.

Will adding the /3GB switch in the boot.ini file resolve this issue?  IF not what else would I change?

Is there a downside in trying to get this last 1GB of RAM?
3 Solutions
You need Windows XP 64Bit in order to fully use all 4GB, and the /3GB will not resolve anything.
There is not much you can do - its down to the way a 32bit OS addresses the RAM. In theory a 32bit OS can address 4Gb but in reality some on that address space is used to control i/o operations etc so isn't available to to be used for memory addressing. The result is that it you put 4Gb in a OC the top bit of memory cannot be used. This typically results in between 3.25 and 3.75Gb  being usable.

see http://www.brianmadden.com/content/article/The-4GB-Windows-Memory-Limit-What-does-it-really-mean-

to make full use of 4Gb you reallt need a 64bit OS.
If you do a search of Experts-Exchange Previously Answered Questions, you will find questions like yours asked MANY MANY times.  I will add my two cents to what Mikkk says above:

From this question:


It's worth noting that WinXP, while the 32-bit version does indeed "support" 4GB, Windows splits the 4 GB of available memory address space into two separate 2 GB address spaces. One of the 2 GB address spaces is used by the Windows operating system, and the other 2 GB address space is used for user mode processes (applications).

However, there is a /3GB switch used in the BOOT.INI file. The /3GB switch changes the memory allocation so that Windows is only allocated 1 GB of address space, and user mode processes are allocated 3 GB of address space. Splitting the address space like this helps Windows to better manage high demand applications. However, Windows is configured to have a 2 GB address space for the operating system for a reason. If you use the /3GB switch, you can severely impact Windows ability to run multiple applications simultaneously.

Also, there is this MSKB article:

The amount of RAM reported by the System Properties dialog box and the System Information tool is less than you expect after you install Windows XP Service Pack 2

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