Arcade Space Invaders

This is a pretty good article, and Space Invaders is a very simple game (as it should be it, it was one of the first!) so it's easy to follow without being over-complicated.

>> The more aliens there are on the screen the longer it takes to get back around to moving the reference alien. At the start of the round there are 55 aliens.

>> That’s 55 interrupts or almost 1 second to move the entire rack. At the end of the round there is only one alien left.

>> It moves 2 pixels left or right 60 times a second. That’s about two seconds from side to side.

This is a good effect and a lot of other Space Invaders clones don't get this right. If you made one in the last 15 years your hardware was likely fast enough to move 50 ships 30 times a second and you didn't have to move one ship per frame. So you didn't get that weird wavy effect to the ship movements like the original arcade version.

Love Space Invaders, here is an HTML5 implementation that you can control with your phone http://www.webdigi.co.uk/fun/space/