Far Travelers is an awesome book about satellites that you can read for free. Much more information than you'd care to know about, it's amazing.
"Another significant improvement included the addition of extra "brain power" to allow the orbiters to perform more complex functions. Viking orbiters possessed two 4096-word, general-purpose computers that could operate in parallel or tandem modes. These replaced the small special purpose computers contained in Mariners 8 and 9. The capability for more rapid picture taking allowed for better site surveys and special regional studies. This capability was augmented by tape recorder systems that could store 2.112 megabits per second, with a capacity of 55 TV pictures-over half a billion bits of information."
"Another significant improvement included the addition of extra "brain power" to allow the orbiters to perform more complex functions. Viking orbiters possessed two 4096-word, general-purpose computers that could operate in parallel or tandem modes. These replaced the small special purpose computers contained in Mariners 8 and 9. The capability for more rapid picture taking allowed for better site surveys and special regional studies. This capability was augmented by tape recorder systems that could store 2.112 megabits per second, with a capacity of 55 TV pictures-over half a billion bits of information."
http://history.nasa.gov/SP-480/ch12.htm
http://history.nasa.gov/SP-480/contents.htm