The Controller Pak is a peripheral for the Nintendo 64 games console made by Nintendo, the Japanese video games Giant. The peripheral is a quite small piece of hardware, about 0.5" by 1.5" by 2". It fits into a slot on the back of the Nintendo 64 controller. It carried on the Nintendo tradition of naming items with the word "pak". Why they decided to leave out the c is unsure, but there is some idle speculation I received from another noder over at my Expansion Pak writeup. Other peripherals to have had the pak suffix are Game Pak, Rumble Pak, Expansion Pak, Jumper Pak, and the Transfer Pak.
The purpose of the Controller Pak was to provide 256k of battery back up memory for save games. Although unlike the other game consoles of the era (Playstation and Saturn) the N64 did not use CDs to store the game, instead cartridges were used. This allowed back up memory for saves to be provided with the game - and it frequently was. This was the problem, and the thing that led to the controller pak being discontinued years before the N64 died - the best games on the system were made by Nintendo themselves and Rare, their second party code wizards. For whatever reason, all (I think) of the games made by these two developers came with battery back up on the cartridge. This meant that the only games which needed a controller pak were somewhat second rate ones made by other companies, with the best of them being Shadow Man and Turok 2: Seeds of Evil. This large lack of demand for the peripheral meant that when I picked up a second hand copy of Shadow Man and went to the shops to get a controller pak, none were available - and this is ages before games stopped being produced for the system.
As with any official peripheral, the market was soon flooded with cheap rip offs from the likes of Gamester. Some offered 1 MB - the same as a Playstation memory card, which was many times bigger than the standard Nintendo version. Some offered Rumble Pak rip offs with the Controller Pak functions built in. All were typically half the price of the official version, but usually the hardware was so sub standard that either the game didn't save at all (some games, such as Acclaim's Turok series, didn't save unless an official Nintendo controller pak was used) or the saves were lost as soon as the machine was turned off. Unfortunately, when the official ones were discontinued, they were the only ones available. I currently have 3 N64 games that I cannot save my progress on.
The controller pak was available from the first day that the N64 was released, but discontinued a few years ago. When it was around it could be bought for £15 in the UK - I'd guess about $20 or so in America. Can anyone give me a more accurate figure?
UPDATE!! Servo5678 has finally laid to rest the whole "Pak" issue with his writeup in Game Pak.
UPDATE!! yerricde has confirmed that the Controller Pak did cost $20 in the States - thanks a lot.
Thanks to jasonm for a grammar correction.
Thanks to yerricde for correcting me on how much memory the controller pak held, and how much it cost.