Developer Prehistoricman recently released Xbox256MB , an advanced modification that allows the original Xbox console’s RAM to be expanded to 256MB , quadrupling its original capacity.
Increasing the memory to 256MB is done by adding an additional address bit to the memory array. The Xbox is already limited in address rows, so the expansion is done on the columns .
To make the RAM fully accessible, you need to write to the NV_PFB_CFG1 register in the console boot code (Xcodes), so as to:
- Enable the additional column bit.
- Configure the AP pin to A9 , correcting the swap between A8 and A9 introduced by the interposer.
Note: This upgrade is intended for advanced users only, as it carries risks and possible stability issues .
To test and flash the RAM, Xblast OS is used , which allows you to test each individual memory chip. The files needed for testing, including the dedicated BIOS, are available on Bitbucket .
To make your system compatible with the new RAM, you need to patch your BIOS using Python 3 and the BIOS_patcher_256MB.py.
This script has been tested on X2 and X3 BIOSes, others are not guaranteed. Some BIOSes, like EvoX, while being able to boot with 256MB of RAM, will not be able to use it without additional patches.
The script allows you to modify the BIOS with the following command:python BIOS_patcher_256MB.py <BIOS file path> [-m] [-d]
- The option
-mreduces the RAM speed from 200MHz to 150MHz to improve stability. To regain lost performance, you can overclock your BIOS before applying the patch, using tools like XBOverclock . - This option modifies the slew and drive trims
-dparameters for the DQS pin, which is useful in case the system becomes unstable.
The script generates a patched BIOS with the suffix .patched256in the file name. Usage example:python BIOS_patcher_256MB.py x2.5035.v16plus.137.bin -m
Interposer PCB for new RAM
The upgrade uses HY5DU573222F-28 memory chips , which are only available in BGA packages. To fit them into the Xbox’s TQFP slot , a PCB interposer is required . Gerber files for manufacturing the boards are available on GitHub.
Two designs have been developed:
- 256Mbit_RAM_interposer_v2_flex – Recommended. Made of flexible PCB for precision and ease of use. The bungee connections on the edges of the board require high tolerance in manufacturing.
- 256Mbit_RAM_interposer_rigidflex – Older version with flexible inner layers that become pins, mimicking the original TQFP package. However, the pins are brittle and tend to lose conductivity due to bending micro-cracks.
Download: Gerbers v1.0
Download: Source code Gerbers v1.0
Source: github.com