Expansion Pak

The Expansion Pak consists of 4 MB (4,194,304 bytes) of random access memory (RAM)—which is RDRAM, the same type of memory used inside the console itself—increasing the Nintendo 64 console's RAM from 4 MB to 8 MB of contiguous main memory. It is installed in a port on top of the console and replaces the pre-installed Jumper Pak, which is simply a RAMBUS terminator.

The Expansion Pak is required for two retail games: Donkey Kong 64 and The Legend of Zelda: Majora’s Mask. Some other games, like Rayman 2: The Great Escape are capable of using the Expansion Pak if available, but do not require it.

Details of how the Expansion Pak is detected are in the RDRAM article.

Hardware

Variations

The Nintendo Expansion Pak went through several PCB revisions. The most notable change was to add in an extra termination resistor to Pin 20 (SIn - Initialization Daisy Chain Input).

Version 1 - (No extra resistor, no bodge)

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  Front side of a Version 1 Expansion Pak (No resistor, no bodge)
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  Back side of a Version 1 Expansion Pak (No resistor, no bodge)

Version 2 - (Bodge from Nintendo)

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  Front side of a Bodged Expansion Pak from Nintendo
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  Back side of a Bodged Expansion Pak from Nintendo

Version 3 - (Resistor added to PCB design)

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  Front side of the modified PCB design that includes the resistor
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  Back side of the modified PCB design that includes the resistor

Open Source Recreation

An open source, 1:1 recreation of the OEM Expansion Pak can be found here complete with pictures and the full KiCad project.

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  Recreated OEM Expansion Pak
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  Electrical schematic for the OEM Expansion Pak
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  Front side of the PCB in KiCad
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  Back side of the PCB in KiCad