Space Invaders 

The first real arcade game, Space Invaders revolutionised trips to the local fair. Instead of hanging around the dodgems, kids started loitering in the arcade section.

The game was straightforward enough - rows of green aliens would wobble slowly back and forth across the screen, dropping down one row every time they reached the edge of the screen. The player had to shoot them.

When the game first started, the computer's weedy CPU struggled to move all of the aliens at once and they crawled across the screen while you moved across the bottom of the screen at a reasonable pace - certainly fast enough to avoid the sluggish alien bullets.

It was only as you started to eliminate aliens (thereby giving the CPU less work to do) that the invaders began moving at a challenging pace.

Eventually Space Invaders was replaced by a whole new generation of "first person shooter" games, such as Galaxian which took the same concept but added multi-directional movement, speed, colour and entertainment to the mix.