I hope this is the correct forum for this question.
In working with HP DC 7600 CMT PCs that each has 4GB of RAM the 3 GB switch will not function on only some of the PCs.
If I add the 3GB switch line into the boot.ini file the PC just does not boot.
I have checked syntax etc to no avail
In windows the PCs display varying amounts of RAM
Some show 3.320 GB others show 3.50 GB and yet others show 3.25 GB. The model PC is consistent as is the type of RAM installed.
My guess is that hardware is reserving addresses during boot up and that causes the issue.
Any help is appreciated.

No need to use any switch. XP will see up to 3.5GB. Depending on the video ram.

The amount of total addressable space allowed by XP is 4GB. That counts graphics card RAM, sound card RAM, and the size of the page file. Diffrent computers with diffrent hardware configs may display a diffrent number than the normally quoted 3.25 GB.

Windows does this automatically, so you don't need to worry about it anyway.

The /3GB switch has nothing to do with making Windows report, utilize, or address more RAM. The /3GB switch is used to give applications more virtual address space, and only applications that explicitly request it (98% of 32-bit applications aren't coded to support this).

Remove the /3GB switch, it can only create problems unless you understand exactly what it does and when to use it (and you don't). The limitation here is the Intel 945 chipset, which no amount of boot switches can overcome or work-around.

An application doesn't need to be "coded" in a special way to use more than 2GB. It is just a bit that needs to be switched. Some are switched, some aren't some you can switch your self, some will crash.

In 64bit Windows, the application would get 4GB with this bit on.

I used the term 'coded' in an over-simplified (though technically inaccurate) sense because I figured that someone who already did not understand what the /3GB switch does probably would get stuck on "set LARGE_ADDRESS_AWARE flag in the image header".

I would disagree with your characterization of how common or prevalent are 32-bit applications with large address support. It is uncommon in the extreme outside of enterprise, database, engineering, scientific, and professional applications. Even within these segments, it is not the norm. I don't know of any that install by default with large address support, and most developers state it is for testing purposes only or not supported in a production environment.

Even Microsoft does not support /3GB (4G Tuning) in a production environment on Windows XP Professional. If you're a developer having problems testing your applications against it, they might take a look. But end-users are on their own.

Given the potential implications for kernel-mode stuff, the risk of application failures because so few 32-bit apps are tested or designed for it, the exceptionally narrow scope where it is indicated or might even prove beneficial, there is little point to indulging its potential merit on a PC running 32-bit consumer OS and applications. One in every ten thousand might realize some benefit or get it working with no apparent adverse consequences.

More and more applications comes with the bit on. It won't hurt anything, it all depends on the users' OS. And as said, if he runs a 64bit OS, it will then automatically get access to 4GB

Really? I would appreciate if you could provide some examples. And we are talking about 32-bit applications and 32-bit OS. Installers that check for 64-bit OS, perhaps (though I doubt all that many more are), since 32-bit applications claiming compatibility under 64-bit OS are almost guaranteed to have been tested in large addressing modes. If they weren't, the developer's testing for compatibility with 64-bit OS was fundamentally incomplete.

Other than crashing the application, the operating system, the risks of data loss that result from crashing applications and operating systems, and failing to boot as the OP clearly reported. Except those things, it won't hurt anything.

That's great. Now if we could only find a discussion that is remotely relevant to 64-bit OS, your repeated mention of it might actually seem much less pointless there.

[quote]Really? I would appreciate if you could provide some examples.[/quotemsg]
Look around the internet.

[quote]And we are talking about 32-bit applications and 32-bit OS.[/quotemsg]
Of course. This doesn't even apply to 64bit applications.

[quote]Other than crashing the application, the operating system, the risks of data loss that result from crashing applications and operating systems, and failing to boot as the OP clearly reported.[/quotemsg]
The bit won't hurt anything by itself. If the user runs a 32bit OS, and he uses the /3GB switch, then it might hurt some places. But the bit alone is harmeless (when I say harmless, then the bit is set by the developer, and therefore assures the app will never crash nomatter how the OS is configured).

[quote]
Now if we could only find a discussion that is remotely relevant to 64-bit OS, your repeated mention of it might actually seem much less pointless there.[/quotemsg]
It is relevant when we talk about how much the bit is used. The developers know that they get 4GB access under 64bit Windows, so they tend to use it more often.