I'm not sure what you mean by "operational computers" unless it means "a computer that isn't broken." Did you perhaps mean "operational amplifier" (op-amp)? An op-amp is a small chip that amplifies a small signal to a larger one. They are used in radios, stereos, MP3 players, TVs, DVD players, and other places where you need to amplify a weak signal (like the pattern of sound reconstructed from the DVD) and produce a lot of current (like for speakers).

A diode is an electronic device which only allows current to flow in one direction. They are sometimes used in electronic equipment to prevent damage if you accidentally insert batteries backward. If the batteries were installed backward, the diode would block current from flowing, so the device would be protected from damage. Diodes are also an important part of most AM radio receivers. In fact, you can build an AM "crystal" radio with just a diode, a pair of headphones, and a coil of wire wrapped around a cardboard tube. The "crystal" is the diode.

A transistor is an electronic switch with 3 pins. If you apply a voltage to one particular pin on the chip, then electrical current is allowed to flow between two other pins. Depending on how you connect transistors together, you can build either digital logic (like calculators and computers) or amplifiers. (Op-amps are made from transistors.) Transistors are the most common electronic device on earth, and the most important. A single Itanium microprocessor chip has 2 billion transistors. So a computer with an Itanium and some memory has more transistors than there are people on earth!