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What is the "/3GB Switch" and how do I set it?

TransMagic utilizes what is called the “/3GB Switch”.  Normally a Windows 32-bit application can only utilize up to 2GB of RAM (both physical and virtual combined).  However, if an application is built with a special set of options it can utilize up to 3GB of RAM – even if your system has only 2GB – the other 1GB will be swap space (hard drive – much slower but still works).  The caveat here is that you also have to tell your OS to utilize this /3GB Switch by manually configuring a couple settings and rebooting.  The extra 1GB makes a huge difference as it’s a 50% RAM increase.  For instructions on setting the /3GB Switch:


For Windows XP or Server 2003:

Go to the Start->Control Panel->Double-Click "System"->Click "Advanced" Tab

At the bottom of the Advanced Dialog in the "Startup and Recovery" section, click "Settings"

At the top of the Startup and Recovery Dialog in the "System Settings" section, click "Edit"

This will open the system's BOOT.INI file. It should look something like:

[boot loader] timeout=30 default=multi(0)disk(0)rdisk(0)partition(2)\WINDOWS [operating systems] multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional" /fastdetect /NoExecute=OptIn

You'll want to copy the last line and edit it so that it looks like the following:

multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional 3GB" /fastdetect /3GB /NoExecute=OptIn

You don't want to replace the last line, you want to add to it so now the BOOT.INI should look something like:

[boot loader] timeout=30 default=multi(0)disk(0)rdisk(0)partition(2)\WINDOWS [operating systems] multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional 3GB" /fastdetect /3GB /NoExecute=OptIn 
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional" /fastdetect /NoExecute=OptIn

Click File->Save and close the text editor. -->Now reboot your system. When your system starts up again, you'll have the option to boot with the /3GB Switch or without it. This is a 50% increase in RAM access and this should make the difference in loading/saving your files.


For Windows Vista or Server 2008:

Go to Start->All Programs->Accessories->Command Promt --> At the command prompt enter:

bcdedit /set IncreaseUserVa 3072

Restart the computer.


Keep in mind that translation is a very RAM intensive process and in order to translate all the geometry it must first all be brought into RAM and then translated.  The RAM limitations of a 32-bit application are not TransMagic bugs but rather Windows 32-bit Operating System imposed limits so there’s nothing TransMagic can do about this.  One thing that can help is to break the assembly into smaller pieces.  A good general rule of thumb when translating geometry is that the data itself will consume 10x the file/assembly size in RAM during translation.  So if you have a 200 MB file/assembly then you can expect that the translation will consume at least 2GB of RAM.

However, the TransMagic R8 series is offered in a native 64-bit support.  This requires that you have a native 64-bit machine, of course.  With native 64-bit support for Windows, theoretically an application would now be able to consume up to 2 Terabytes of RAM.  Although 2TB machines don’t exist yet 64-bit machines with large quantieis of RAM are certainly available now.  64-bit TransMagic on a 64-bit machine eliminates the need for the 3GB Switch.

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