The Expansion Pak (拡張パック ,Kakuchō Pakku) allows the random access memory (RAM) of the Nintendo 64 console to increase from 4MB (megabytes) to 8MB of contiguous main memory. Game developers can take advantage of the increased memory in several ways, including making games that are more visually appealing. The add-on was released in 1998 and contains 4 MB RDRA, the same type of memory used inside the console itself. By increasing system memory, there is potential for enhancements to games designed with the added RAM storage in mind. The Expansion Pak is installed in a port on top of the Nintendo 64 and replaces the pre-installed Jumper Pak, which is simply a RAMBUS terminator.A few games, including Rare's Donkey Kong 64 and Nintendo's The Legend of Zelda: Majora's Mask require it to run. Capcom's Resident Evil 2 used the Expansion Pak for making areas of the game and monsters more detailed. Perfect Dark had limited gameplay options when the Expansion Pak was not present. Supporting games usually offered higher video resolutions or higher textures and/or higher color depth. For example, the Nintendo 64 all-remade version of Quake II features higher color depth but not a higher resolution when using the Expansion Pak. It was used in StarCraft 64 to unlock levels from the popular Brood War add-on for the PC version of the game. Many games such as Castlevania: Legacy of Darkness and Indiana Jones and the Infernal Machine optionally used the Expansion Pak to add a high resolution 640x480 display mode for games, while other games saw the benefit of a smoother frame rate. The Expansion Pak was available separately as well as bundled with Donkey Kong 64. In Japan, the Expansion Pak was additionally bundled with Zelda: Majora's Mask and Perfect Dark, though the games were also available separately in other regions.
The RAM in the expansion pack runs at a slower speed than the system RAM due to increased latencies in accessing the accessory. It is therefore less useful than simply doubling the amount of RAM.