The Expansion Pak (Expansion Pack) allows the random access memory (RAM) of the Nintendo 64 console to increase from 4 MB (megabytes) to 8 MB of contiguous main memory.[8] With the help of an included key, the Expansion Pak fits into the slot that is below a removable panel on the top of the N64 console. Game developers can take advantage of the increased memory in several ways, including making games that are more visually appealing.[9] The add-on was released in 1999 and contains 4 MB RDRAM, the same type of memory used inside the console itself.[1][8] 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.[7][8]

A few games, including Rare's Donkey Kong 64 and Nintendo's The Legend of Zelda: Majora's Mask required it for play.[10] Perfect Dark had limited gameplay options when the expansion pak was not present.[9] 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 2 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. 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 could be purchased alone as well.