Adafruit has built its own distribution for the Raspberry Pi in order to build in kernel modules that support the special hardware features of the RasPi. It needs a 4 GB memory card to run. See the Occidentalis v0.2 announcement. Of course, with a $40 class PC, why not use it as a microcontroller?
On the other hand is the ChipKit, which costs about the same but is an actual microcontroller (mcu). That means it doesn’t run on a full fledged operating system like Linux but rather on firmware. On computers, people write applications while on microcontrollers people write code to run on ‘bare metal.’ That means the mcu software designer has full control over timing and configuration of the hardware. The ChipKit runs at about a tenth the Raspi clock with memory measured in KB rather than MB but doesn’t need external storage for persistent memory.
So you can just use a computer if all you need is a bit of hardware control or you can use a microcontroller if you need the hardware control without complex software. Or, if you want to go to town, you can use both – like a chipKIT PI development board by element14. This gets back to the original purpose of the mcu – a hardware interface for a computer peripheral.
The you get back to the Arduino class, 8 bit mcu. Nobody is really serious about 8 bit computers, anymore, but the 8 bit mcu is replacing the 555 timer as the chip for general purpose these days, it seems. You can get an 8 bit mcu for about the cost of a 555 timer chip and then use software to control the oscillation rate rather than discreet resistors and capacitors. The hardware has moved into software.
so many choices; so many options; and so many are really rather cheap as well as capable. No wonder it is a wonderland for robotics and control device hacking.
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