In ATItool click settings and select "Miscellaneous".
Click the button that says “Save VGA Bios to file...”. Give the file a simple name like “12pipe.bin”. This will be your backup copy.
Make a second copy, which will be modified, and name it something like “16pipe.bin”.
Download the hex editor from this website (I would recommend using the “stable” version instead of the beta version):
http://www.mh-nexus.de/programs.htm#HxD
This software will allow you to modify your bios to enable the pipelines.
Extract the hex editor program and run it. Open “16pipe.bin”.
Find the row marked 00000070 and the column labeled ‘A’. You should find ‘61’ at that location. The second bit represents the number of disabled pixel pipe quads. Change the data value to ‘60’ to enable all 16 pixel pipes.
Note: If you ever get bord later you can mess around with disabling pipes. 1 means four pipes are disabled (X800GTO), 2 means eight pipes are disabled (X800GT), 3 means twelve pipes are disabled (yep only 4 left active).
Save the modified bios and exit the hex editor.
The next part of the process is creating a bootable device (floppy, CD, or USB flash drive) which will be used to flash VGA Bios. I used a floppy because it is easy.
For detailed information on how to do these things go to this link and read about flashing your VGA Bios:
http://www.techpowerup.com/articles/overclocking/vidcard/34
This link contains instructions for creating a bootable USB flashdrive if a floppy is not an option.
I recommend using ATIflash if you plan to do it in DOS.
You can download it at the bottom of this page:
http://www.techpowerup.com/bios/
I used version 3.09
You will want to put the contents of the ATIflash archive onto the bootable media as well as the two bios files (the backup copy and the new unlocked version).
Boot into DOS and type the following command at the prompt:
atiflash.exe -p 0 16pipe.bin
Note: This assumes that you followed my naming conventions.