Space! | Classic retro game for the Commodore PET Computer (1979)

PACE! is a simple space shooting game. Use the number pad to move your crosshairs across the independently-scrolling starfield and press SHIFT to shoot. Targeting is tricky and only a precise hit will take down the enemy ships. Your continuously-depleting energy—needed both for flying and firing your laser—imposes a strict time limit. A machine-language subroutine placed in the cassette buffer allows the background starfield to scroll in all directions as you move your crosshairs. Overall, this is a solid and challenging game for the time.

There is a problem, though: SPACE! is only playable on early PETs. If you try to play the game on, say, a 4016, you won't be able to control your movements, because the keyboard-reading subroutine depends upon the results of PEEK(151) (the program corrects this PEEK to look at memory location 515 on first revision ROMs), and different models of PET/CBM decdode the keyboard matrix with different values. Jim Butterfield discouraged the use of PEEK(151) to read the keyboard becuase of the compatability issues that result.