Compare and contrast the characteristics and functionalities of address buses, data buses, and control buses?

Address bus

It selects the one location that the CPU wants. With $n$ address lines, the CPU can address $2^n$ locations. For example, 16 lines give $2^{16} = 65536$ locations, that is 64 K.

Data bus

It carries the word that is read or written. A 32-bit data bus moves 32 bits in one transfer. A wider data bus gives a faster system.

Control bus

It carries signals like memory read, memory write, I/O read, I/O write, clock, interrupt request and bus grant. It tells all the units when and how to use the address and data buses. In short, the address bus says where, the data bus says what, and the control bus says when and how.

Example of how they work together

Suppose the CPU wants to read a word from memory. It places the address on the address bus. It then activates the memory read signal on the control bus. The memory finds the location and puts the word on the data bus. The CPU takes the word from the data bus. For a write, the CPU puts the address on the address bus and the data on the data bus, and the control bus carries the memory write signal. All three buses are therefore needed in every transfer, and a fault in any one of them stops the system.