Miscellaneous

Many computers also contain internal "helper" chips which can't really be classified as CPU, memory, or i/o device. These include:

Floating Point Units (or FPUs) that are specialized to perform floating point (real number as opposed to integer) calculations.
Signal processing chips that perform fast fourier transforms and other common signal processing routines.
Memory management units that coordinate all the different RAM chips, ROM chips, and memory mapped i/o into one unified address space.