Multiple choiceQuestion 1 · Recall
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By the end you can name the three buses, say what each one carries and in which direction, and describe a memory read or write in terms of buses.
The CPU, memory and the devices are joined by a bus: a bundle of parallel wires shared by every component connected to it.
There are always three buses, and the trick is remembering what travels on each:
| Bus | Carries | Direction |
|---|---|---|
| Address bus | The location being accessed — a memory or device address | Usually one way: CPU → memory/devices |
| Data bus | The actual data being read or written | Both ways: in and out |
| Control bus | Control signals — read/write commands, the clock signal, interrupt requests, acknowledgements | Both ways |
The width of a bus is how many wires it has, so how many bits it carries at once. A 64-bit data bus moves 64 bits per transfer.
Bus
A set of parallel electrical connections (wires) that carries addresses, data or control signals between the CPU, main memory and the peripheral devices.
Worked example: Reading a value from memory
The CPU needs the value stored at memory address 600. Describe the transfer using the three buses.