Originally designed for a run of 5 years, but the engineers explicitly designed for longevity. It's been a few decades now!
Multiple onboard computers for redundancy, including voting to elect a leader. (!)
No OS, programmed in Assembly and maybe Fortran.
The main computing unit is interrupt based, and uses them to receive inputs from other subsystems.
Memory is magnetic fields on a wire. Slow, but non-volatile and resistant to radiation.
Golay encoding to reduce the error rate.
There's a tape deck that can store 500Mbits as a backup, but all captured data is instantly fired off to Earth to save space.
Bandwidth decreases the further away it gets. Compression was added to it midflight so it could use the bandwidth more effectively. 😯
Probably can't reach it after 5 years. It's powered by a plutonium RTG, which will reach its half life soon.