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NMC - original by MadBoris

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About this mod

May help with crashing/performance issues in FO3 particularly when using my larger texture packs by allowing FO3 more address memory space. Originally programmed by MadBoris for Supreme Commander, I have simply tweaked it to work with Fallout 3. Compatible with latest FOSE but NOT compatible with WindowsLIVE. Not required for GOG Version of FO3.

Permissions and credits
FOSE from 1.1 beta 8 onwards is compatible with this mod

NOTE: Not compatible with Games For Windows LIVE.

*** This mod is not required if you are using the GOG version of FO3, as GOG have already made their release Large Address Aware ***

For DLC Issues:

If the DLCs are already in the DATA folder: when starting up the game, go into data files on the launcher and check them again.

Cannot find any Game Saves?

Go into the save folder, and pull the files out of your profile, and put in just the SAVES folder, NOT the one for your profile.

(Thanks to creedofheresy for the information!


I am releasing this application as it may help with crashing and performance issues with Fallout 3, particularly when using my larger texture packs. The utility was originally programmed and released by MadBoris, for the game Supreme Commander. I (NMC) have simply tweaked the program to work with Fallout 3. Read all about the original utility here: .


It is a good practice to specify large-address-aware for 32-bit applications (such as Fallout 3), by using the linker flag /LARGEADDRESSAWARE, *even if the application is not intended for a 64-bit platform*, because of the advantages that are gained at no cost. (Info From Microsoft)

Enabling this large-address-aware flag for software allows a 32-bit program to access more memory (with special boot options on a 32-bit OS or on a 64-bit OS- see instructions below)... In general, enabling the /LARGEADDRESSAWARE flag is a good practice, which is not enabled in Fallout 3.

That is what this utility does; it adds makes Fallout 3 'large-address-aware'. However. you also need to enable the '3gb switch' (except in Vista 64 bit).

Background info:

Regardless of the amount of physical memory in your system, Windows uses a virtual address space of 4 GB, with 2 GB allocated to user-mode processes (for example, applications) and 2 GB allocated to kernel-mode processes (for example, the operating system and kernel-mode drivers).

On systems that have 1 GB or more of physical memory, these two startup switches (see below), can be used to allocate more memory to applications (3 GB) and less memory to the operating system (1 GB). This additional virtual address space helps reduce the amount of memory fragmentation in the virtual address space of the Exchange information store process.

So, what does this mean? Well...

* Fallout 3 (WITHOUT the 3gb switch and NOT large Address Aware) on 32-bit platforms can address up to only 2 GB.

* Fallout 3 with the /LARGEADDRESSAWARE:YES linker flag on 32-bit Windows XP with the special /3gb * boot option can address up to 3 GB, ie an extra 1GB.(This however, limits the kernel to only 1 GB which may cause some drivers and/or services to fail- but not so much a problem with XP than Vista 32bit).

* Fallout 3 with the /LARGEADDRESSAWARE:YES linker flag on 32-bit versions of Windows Vista, can address memory up to the number specified by the boot configuration data (BCD) element "IncreaseUserVa". IncreaseUserVa can have a value ranging from 2048, the default, to 3072 (which matches the amount of memory configured by the /3gb boot option on Windows XP). I advise using IncreaseUserVa 2900.
(The remainder of 4 GB is allocated to the kernel and can result in failing driver and service configurations. This issue has since been addressed by microsoft via OS updates)

* Fallout 3 on 64-bit platforms can address up to 2 GB, or up to 4 GB with the /LARGEADDRESSAWARE:YES linker flag. So, 64-bit processors provide a huge leap in the amount of physical and virtual memory that can be addressed.


*****So, cut to the chase, what now?*****
1) Make Fallout 3 'large address aware using this utility.

Follow the video to Complete Part 1 of the install. If you are using a 64bit version of Windows, then just follow the video and you are done.

So, you should have completed the following:

a) make a back up copy of 'Fallout 3.exe'.
b) put Fallout3.exe in the '3GB enabler' folder
c) double click 'START.BAT'
d) follow the instruction in the command window
e) once made 'large Address aware', return the fallout3.exe to your game folder.

If you are using a 64 Bit operating system (xp, Vista or Windows 7), you are Done!

PART 2- Required for 32bit operating systems ONLY.
2) Enable the /3GB switch on your computer. The switch is entered in the system’s boot.ini file and takes effect after a computer restart. Here's how to do it:

(....WARNING: From MADBORIS himself;

"I only suggest this for people that are intermediate to advanced users, so if you don't feel comfortable editing a boot.ini, you may not want to proceed. Editing a boot.ini improperly may render your PC unbootable, which is why I suggest you copy/paste the entry in the boot.ini to make a new additional boot option, leaving the original intact.")

OK, disclaimer over, what next!?

***For Windows XP***

Right-click My Computer and select Properties. The System Properties dialog box will appear.

a) Click the Advanced tab.

b) In the Startup and Recovery area, click Settings. The Startup and Recovery dialog box will appear.

c) In the System startup area, click Edit. This will open the Windows boot.ini file in Notepad.

d) In the [Operating Systems] section, add the following switches to the end of the startup line that includes the /fastdetect switch: " /3GB /Userva=2900" (do not include the quotes)

e) Save the changes and close Notepad.

f) Click 'OK' two times to close the open dialog boxes, and then restart the computer for the change to take effect.

***To turn off the 3GB switch***

Remove: "/3GB /Userva=2900" from the startup line.


***To enable the 3GB switch on Windows Vista™ 32bit-


a) Right-click Command Prompt in the Accessories program group of the Start menu.

b) Click Run as Administrator.

c) At the command prompt, enter "bcdedit /set increaseuserva 3072". You should see a message saying this was successful.

d) Restart the computer.

***To turn off the 3GB switch***

a) Right-click on Command Prompt in the Accessories program group of the Start menu. Click Run as Administrator.

b) At the command prompt, enter "bcdedit /deletevalue increaseuserva"

c) Restart the computer.

***Important hotfix for Vista Users***

(Vista's handling of video memory mapping was duplicating address space consumption with an applications private video memory mapping, therefore you may run out of address space sooner, especially with larger amounts of memory available on modern video cards):

For more information on the 3GB switch, refer to the following Microsoft MSDN article:


Credits: The genius of MadBoris, for programming this utility. Read about it all here:

Me, for tweaking it for use with fallout 3!