Feb 222012


32 bit processes are by default confined to a 2 GB address space even though a 32 bit address can address up to 4 GB of memory. Remaining 2 GB goes to the Windows Kernel. With LARGEADDRESSAWARE we can bypass this limitation to an extent, this switch will enable a 32 bit process to address up to 3 GB of virtual address space.

The downside of this feature is that Kernel components will be restricted to 1 GB of virtual address space. We advise developers to use this switch only on server machines where just one dedicated application is set to run, for e.g. SQL Server. Its not great to halve kernel memory space on a machine with too many user mode applications or device drivers running in tandem as there will be demand for higher amount of kernel memory.

On Windows XP, some drivers, especially video adapter drivers with onboard RAM, cannot run with the /3GB parameter because they require more address space than the 1 GB kernel address space permits.

While on a 64 bit machine, considering the vast expanse of memory available to us, LARGEADDRESSAWARE flag is turned on by default for a process this way a 32 bit process gets the entire 4 GB address space on a 64 bit machine. Well known desktop 32bit applications like Visual Studio has this switch enabled because most of the new machines we purchase are 64 bit machines and this way Visual Studio benefits automatically. This switch is harmless on a 32 bit machine which doesn’t have /3GB OS switch enabled.



The command to enable large address aware is as follows…


How to check if the above command worked or not? Run the above executable (in our case NotePad.exe) with DumpBin.exe.

C:\> DumpBin /Headers NotePad.exe

14C machine (x86)
4 number of sections
4BA1DC16 time date stamp Thu Mar 18 02:53:58 2010
0 file pointer to symbol table
0 number of symbols
E0 size of optional header
122 characteristics
Application can handle large (>2GB) addresses
32 bit word machine

See highlighted line.

Changes to boot.ini

Please add /3GB switch as shown below to a boot entry that you’d like to configure…

multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Windows Server 2003, Enterprise" /fastdetect /3GB