The Controller Pak (NUS-004) is the console's memory card, comparable to those seen in the PlayStation and other CD-ROM-based video game consoles. Certain games allow saving of game files to the Controller Pak, which plugs into the back of the Nintendo 64 controller. The Controller Pak was marketed as a way to exchange data with other Nintendo 64 owners, since information saved on the game cartridge can not be transferred between cartridges.

It is plugged into the controller and allows the player to save game progress and configuration. The original models from Nintendo offered 256 kilobits (32KB) battery-backed SRAM, split into 123 pages with a limitation of 16 save files. The number of pages that a game occupies varies, sometimes using the entire card. It is powered by a common CR2032 battery.

Upon launch, the Controller Pak was initially useful, and even necessary for earlier Nintendo 64 games. Over time, the Controller Pak lost popularity to the convenience of a battery backed SRAM or EEPROM found in some cartridges. Because the Nintendo 64 uses a Game Pak cartridge format that allows saving data on the cartridge itself, few first party and second party games use the Controller Pak. The vast majority are from third-party developers. This is most likely due to the increased production and retail costs which would have been caused by including self-contained data on the cartridge.

Some games use it to save optional data that is too large for the cartridge, such as Mario Kart 64, which uses 121 of the total 123 pages for storing ghost data, or International Superstar Soccer 64, which uses up the entire cartridge's space for its save data. Tony Hawk's Pro Skater uses 11 pages. Quest 64 and Mystical Ninja Starring Goemon use the Controller Pak exclusively for saved data. The Japan-only game Animal Forest uses the Controller Pak to travel to other towns.