To enable SLI in GTAIV you need to download this softaware:
http://www.geeks3d.com/20100528/manage-your-sli-profiles-with-nvidia-geforce-...2. Install it, drag, drop, whatever you need to do.
3. Open the program and then export the settings to a folder of your choosing.
4. Rename the text file to create a backup just in case something goes wrong.
5. Repeat the export process to create the new notepad file you will be editing. Then open it.
6. Find (Ctrl+F) "Grand Theft Auto 4" . Once you find it you will see some executable command lines
and compatibility template codes and will look something like this:
Profile "Grand Theft Auto 4"
ShowOn GeForce
ProfileType Application
Executable "gtaiv.exe"
Executable "launchgtaiv.exe"
Setting ID_0x0095def9 = 0x00000202
Setting ID_0x1033cec1 = 0x00000003
Setting ID_0x1033dcd2 = 0x00000004
Setting ID_0x1095def8 = 0x00400405
Setting ID_0x10ecdb82 = 0x00000001
EndProfile
7.GTA: EFLC seems to be compatible with SLI even though they use the same engine and version of it,
at least with using the all the GPU processors, the VRAM ball is still dropped though. If you look
you will see that the EFLC profile right below is missing that final setting line:
Setting ID_0x10ecdb82 = 0x00000001
Delete it and save your profiles.
8. Return to your Profile Manager and click import. Import the new profile file (not the back up).
Play the game and enjoy
Quelle