As Jan Hudec mentioned, advances in computing mean that off-the-shelf commercial processors offer plenty of computing power for use in UAVs or other aircraft.
Looking at a couple of examples:
The Rockwell Collins IPC-8303 computer uses an Intel Pentium-M 738 at 1.4 GHz, 2 MB L2 cache, 10 watts. There is also a PowerPC option.
The Rockwell Collins FMC-4000 mission computer is able to accommodate a variety of processors:
- Quad core PPC 1.5 GHz
- Dual core PPC 1.3 GHz
- Single core PPC 7448 1.3 GHz
- Single core PPC 8315E 600 MHz
They also mention that other components such as Intel Atoms or i7 Dual/Quad core processors can be added.
The amount of information processed by these computers has increased along with their power. The FMC-4000 can use a 10-gigabit uplink. Modern computers are designed to process all kinds of sensor data. For aircraft like the MQ-1 or especially the RQ-4, there are many sensors, including video data, feeding into these computers. They are capable of much more than the first flight computers.
Also mentioned by Jan Hudec, the key in aerospace systems is redundancy. Each subsystem is generally controlled by multiple computers. This ensures both accuracy and reliability, and prevents the whole system from going down due to one computer failing.