Space Invaders Codes and Secrets (PSX)

The home version of Space Invaders for the Atari 2600 was a huge success. It offered 112 different versions of the game. Variations included invisible invaders, invisible missiles and other subtle alterations. It was not the first video arcade adaptation for the Atari 2600 system (most of the early games for the 2600 were adaptations of early Atari video arcade games such as Breakout, Pong, Night Driver, etc.), but it was the first officially licensed arcade game for home conversion from one company to another (in this case, Taito to Atari.) The game was the breakthrough for the popularity for the Atari 2600. Other home console companies would make their own conversions of Space Invaders. Examples included Space Armada for the Intellivision, Alien Invaders.

Plus! for the Odyssey 2 and TI Invaders for the TI-99/4A. But only Atari and Bally owned the rights to the use of the title Space Invaders. The console had been released in 1977, but sales of the 2600 skyrocketed during the 1980 holiday shopping season, as millions of families bought the Atari system just so that they could play Space Invaders. This marked the beginning of home video adaptations of popular arcade games. Space Invaders was also available for the Atari 8-bit family of home computers. (Wikipedia)

Codes

Misc. Codes
While paused press Down, Left, Circle, Down, Right, Right, Right - Five Shots

Pause the game and press Right, Right, Right, Down, Circle, Left, Down - Nine lives

Unlockables

Unlock Classic Mode and Maniacal Difficulty
Classic Mode is the original black-and-white Space Invaders.

Maniacal Difficulty is a mode that makes everything (except special weapons) move a lot faster!

Classic Space Invaders - Beat the game on Normal Difficulty.

Maniacal Difficulty - Beat the game on Expert Difficulty.

Secrets

Level Select and Classic Mode
At the main menu, press Circle and a level select menu will appear. If you go to Level 00, you'll fight a retro boss, and once you defeat this boss, a new option will open up, allowing you to play in Classic Space Invaders Mode.

One speedy gameplay session right here: