Buses

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Quick Questions

Shade in the A or B circle for each question.

1. What is a bus in a computer?

A A type of memory that stores programs permanently

B A set of wires that carries data, addresses or signals between components

2. Which component does a bus connect to the CPU?

A RAM

B A bus never connects to the CPU

3. How many kinds of bus are in the Von Neumann model?

A Three: address bus, data bus and control bus

B One: a single bus does every job

4. Which bus carries the memory address of the location to be read or written?

A Address bus

B Data bus

5. A bus has 32 wires and another has 64 wires. Which can carry more bits at once?

A The 32-wire bus

B The 64-wire bus

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1address bus		AA bus is a set of wires, not a single wire, and it connects many components such as the CPU and RAM.
2data bus		B32-bit data bus vs 8-bit data bus
3A bus carries control signals, such as read and write, to coordinate the components of a computer		CThe address bus carries addresses, not data. Data travels on the data bus.
4A bus with more wires can carry more bits at the same time, so more data moves in each transfer		DCarries data and instructions between the CPU, RAM and other components, in both directions
5The address bus carries data from RAM back to the CPU		Econtrol bus
6A bus is a single wire that connects the CPU to the keyboard only		FCarries the address of a memory location from the CPU to RAM, in one direction only

Definitions

bus

Fill in the Blanks

Complete each line of code by filling in the missing parts.

___ = wires linking the CPU, RAM and I/O

The _______ bus carries locations in RAM

The _______ bus carries read and write signals

A bus with 16 wires carries __ bits at once

RAM -> ____ bus -> MDR

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A PC ← 100

B MAR ← PC

C SEND MAR ON DATA BUS

D MDR ← DATA BUS

Question 2

A ADDRESS BUS: TWO WAYS

B DATA BUS: TWO WAYS

C CONTROL BUS: CARRIES SIGNALS

Question 3

A wires ← 32

B bits_at_once ← 1

C OUTPUT bits_at_once

Question 4

A CPU WRITES 7 TO RAM

B SEND ADDRESS ON ADDRESS BUS

C SEND VALUE ON ADDRESS BUS

D SEND WRITE ON CONTROL BUS

Question 5

A BUS 1 ← 'ADDRESS'

B BUS 2 ← 'PROGRAM'

C BUS 3 ← 'CONTROL'

Answer Key

Buses

Section A: Quick Questions

B — A set of wires that carries data, addresses or signals between components

A — RAM

A — Three: address bus, data bus and control bus

A — Address bus

B — The 64-wire bus

Section B: Match the Pairs

address bus → Carries the address of a memory location from the CPU to RAM, in one direction only

data bus → Carries data and instructions between the CPU, RAM and other components, in both directions

A bus carries control signals, such as read and write, to coordinate the components of a computer → control bus

A bus with more wires can carry more bits at the same time, so more data moves in each transfer → 32-bit data bus vs 8-bit data bus

The address bus carries data from RAM back to the CPU → The address bus carries addresses, not data. Data travels on the data bus.

A bus is a single wire that connects the CPU to the keyboard only → A bus is a set of wires, not a single wire, and it connects many components such as the CPU and RAM.

Section C: Definitions

bus — A set of wires that carries data, addresses or control signals between the CPU, RAM and other components. More wires means more bits can be carried at once.

Section D: Fill in the Blanks

bus = wires linking the CPU, RAM and I/O

The address bus carries locations in RAM

The control
 bus carries read and write signals

A bus with 16 wires carries 16 bits at once

RAM -> data bus -> MDR

Section E: Spot the Error

C — The MAR holds a memory address, and addresses travel on the address bus, not the data bus. The line should be SEND MAR ON ADDRESS BUS.

A — The address bus is one-way: the CPU sends addresses to RAM, and RAM never sends addresses back. It should say ONE WAY.

B — Each wire carries one bit, so the number of bits carried at once equals the number of wires. 32 wires carry 32 bits, so the line should be bits_at_once ← wires.

C — The value being written is data, so it travels on the data bus. The address bus only carries the location. The line should be SEND VALUE ON DATA BUS.

B — The three kinds of bus are the address bus, the data bus and the control bus. There is no program bus, so line 2 should be BUS 2 ← 'DATA'.