None. Valves are not used. Integrated circuits are now the mainstay of most electronic devices.
They haven't been replaced! Only now they are much smaller and switched on and off by nano-bots that receive instructions from user input.
Just like the valves used in valve stereo equipment or old radios. Except in computers (like the transistors in modern computers) valves are usually driven fully into saturation and cutoff, while in a valve stereo or old radio valves are usually operated as linear amplifiers with minimal distortion.
Billions.
Valves, as used in an old wireless/radio, is not used in modern computers.
All modern vehicles are complex electronic systems. Computers and electronics do nearly everything, from controlling ignition, fuel, valves, etc.
The lowprice and flexability of modern computers allow many businessesandorginizations to place terminals in many differentlocations.
vaccum tubes and valves.
Computers.
There are no valves in a modern computer. If by valves you mean vacuum tubes, the equivalent is a transistor. Modern CPUs have many transistors/gates on their dies. The SandyBridge i7, a near-top end general purpose computer COU can have 2.2 billon transistor elements on the CPU die. Of course there are many more transistors incorporated in the logic chips, controllers and video cards in a computer as well.
Modern Apple computers are referenced to as Mac computers or Macintosh computers
Because - when Colossus was built (in 1943), microchips had yet to be invented ! Microchips replaced valves and transistors in newer computers.
Modern Apple computers are referenced to as Mac computers or Macintosh computers