Controller Pak

This is a list of accessories for the Nintendo 64 video game console.

The Nintendo 64 controller is an "m"-shaped controller with 10 buttons (A, B, C-Up, C-Down, C-Left, C-Right, L, R, Z, and Start), one analog stick in the center, a digital directional pad on the left hand side, and an extension port on the back for many of the system's accessories. Initially available in seven colors (gray, yellow, green, red, blue, purple, and black), it was later released in transparent versions of said colors (except gray). The N64 pad's analog stick is notorious for wearing out quickly, eventually becoming unable to return to centre position (though they often still functioned normally). Also, the analog stick would become uncalibrated if not centered properly when the system was booted up; if the stick was not centered, the game would calibrate with the altered position at "zero". Because this may not be discovered until the player enters the game, a universal software recentering method is printed in every manual (simultaneously pressing the L, R, and START buttons). Early titles such as Wonder Project J2: Koruro no Mori no Josette would lose calibration if the player moved the cursor while accessing the Controller Pak save. This feature could be used to cheat in some games. In Doom, when the stick is held down when calibrating, the player will be able to run faster when pushing the stick up.

On a side note, this is the last official Nintendo Controller to use standard Phillips screws. Starting with the GameCube, tri-wing screws have been used for security.

The Controller Pak (コントローラパック, Kontorōra Pakku^?) is the console's memory card, comparable to those seen in the PlayStation and other CD-ROM-based video game consoles. Certain games allowed saving of game files to the Controller Pak, which plugged into the back of the Nintendo 64 controller (as did the Rumble and Transfer Paks). The Controller Pak was marketed as a way to exchange data with other Nintendo 64 owners, since information saved on the game cartridge could not be transferred to another cartridge.

...
Wikipedia