Parsec is a straightforward scramble-and-defend game with no option to reverse direction (as you have in Defender) and no bombs (which you have in Scramble).
The control keys present serious problems for those without joysticks, and you just have to fiddle about until you find the best compromise.
The graphics are adequate, and the landscape over which you fly is varied, if rather uninspired. There is a freeze command for when the milk boils over, and, if you have the Texas Instruments speech synthesizer unit, the game will give you verbal status reports.
There are 16 levels of play, and you have four lives. As you move through the different screens, you encounter seven different enemies and asteroid belts, all of which get speedier as the game progresses.
Parsec appears hopelessly out of date in comparison with games currently available on other machines, although some will no doubt still enjoy it.