"CPU runs at a leisurely 200 MHz, which seems slow to us. While Curiosity just landed, design work started years before, during the 2004 to 2008 period. Spacecraft are not produced overnight. Once a design is committed, the software is written and checked many times for flaws. Using the latest hardware and software would allow undiscovered bugs to pass through, threatening the mission. Ever since Apollo, NASA has depended on late-model, low-end CPUs to do the heavy lifting for its missions."

Macs in Space: Curiosity Rover Based on G3 Processor

According to ExtremeTech, NASA’s Curiosity rover is powered by a RAD750 motherboard that contains a PowerPC 750 CPU, which is equivalent to a PowerPC G3 in the Mac world.

http://lowendmac.com/2012/macs-in-space-curiosity-rover-based-on-g3-processor/