It is always entertaining to read about spacecraft's computer systems. They are radically different from mainstream commercial PC technology. The keyword to enter in Google search is: Embedded Computer System on the Rosetta Spacecraft. It will find a PDF scientific paper that describes the Rosetta computers.
The lander (Philae) main CPU is the 16 bit Harris RTX2010 (datasheet available on internet), introduced on the market in the early '90. The spacecraft system bus is running at a whopping 32kbit/s; there is less than 1 Mb of RAM; all the embedeed code has been written in forth language, on a computer architecture that has been last updated 30 years ago.
This is thousand times slower than a smartphone, and still enough for the task at hand.
This isn't my main area of study (nor is it even in the right field as me except for sharing "Engineering" in the name) so anyone feel free to correct me if I'm wrong. But from what I recall and understand is that this hardware is first radiation hardened, an incredibly expensive and difficult process (this is where Material Sciences comes into play, and it's not like "put a layer of clear film on top of it" easy or simple but pretty intensive where VLSI designs comes into play). In addition, all of the code is pretty bare-bone optimized. In a sense, our hardware today has layers and layers of hardware and software on top of it to help it understand how to execute a function on a diverse set of hardware, allowing us to run the same programs from 1998 on 2014 hardware. Because these hardware was designed for this specific task, they don't have to worry about supporting different hardware. It makes the job so much easier and essentially allows you to "optimize" everything (tailor everything to that hardware). The hardware also has proven itself to work, so why not recycle part here and there when you can?
Space Programs are the original users of the Low End Box. Like the hardware they used for the moon missions, haha!
Source: A long (*cough* drunken *cough*) conversation with several Aerospace Engineers, Electrical Engineers, and Computer Scientists who wanted to pursue careers at NASA and other space agencies.
