Surplus goods are generally cheaper then new stuff, but only if you can easily find them. A switch is an electrical, electronical or mechanical device to interrupt or conduct an electrical current . Synchronous circuits are circuits that work in time steps under the control of a clock . An example of a synchronous circuit is an MCU or MPU . You can regard a synchronous circuit as asynchronous stages with registers between the stages.
Synchronous circuits are usually much more complex than asynchronous ones.
When only one clock circuit is used for all registers, the slowest stage determines the maximum clock speed . When you're looking for a serious amount of scarce chips click this.