Central Processing Unit (CPU) Architecture (Cambridge International A-Level Computer Science): Exam Questions

A computer system has a dual-core Central Processing Unit (CPU).

State the purpose of the system clock and the Control Unit (CU) in a CPU.

(i) The number of cores in the processor affects the performance of the computer system.

Identify one other feature of a processor that can affect the performance of a computer system and state why it affects the performance.

(ii) A solid state (flash) memory drive is automatically recognised by the computer when it is plugged into a port in the computer.

Identify an appropriate type of port to connect the solid state memory drive to the computer.

Explain how this port provides an automatic connection.

A computer designed using the Von Neumann model for a computer system contains general purpose registers and special purpose registers.

Describe the purpose of the Status Register (SR).

Identify two differences between general purpose registers and special purpose registers.

A student has a computer.

The computer is designed using the Von Neumann model for a computer system.

Complete the table by describing the purpose of each of the given registers.

The student needs to connect the computer to a monitor that has a screen resolution of 2560 × 1600 pixels. The monitor also has built-in speakers.

The computer has a Video Graphics Array (VGA) port and a High Definition Multimedia Interface (HDMI) port.

Explain the benefits of connecting the monitor to the computer using the HDMI port instead of the VGA port.

The Central Processing Unit (CPU) of the basic Von Neumann model for a computer system contains several special purpose registers.

The Memory Data Register (MDR), Index Register (IX) and the Accumulator (ACC) are examples of special purpose registers.

Identify two other special purpose registers and state their role in the CPU.

A computer has a single 2.1GHz CPU.

(i) Describe how increasing the clock speed to 4GHz can increase the performance of the computer.

(ii) A second computer has a CPU with two 2.1GHz cores.

Explain why the second computer does not always run twice as fast as the computer with one 2.1GHz CPU.

An optical disc reader/writer is connected to the computer.

Give the name of one port that can provide a connection for the optical disc reader/writer.

Identify one port that could be used to connect the virtual reality headset to the laptop.

Justify your choice.

A computer system is designed using the basic Von Neumann model.

Registers and buses are components in the Von Neumann model.

(i) Identify three other components in the Von Neumann model of a computer system.

Do not include registers or buses in your answers.

(ii) Identify two differences between special purpose registers and general purpose registers.

The following incomplete table contains steps of the Fetch‑Execute (F‑E) cycle and their descriptions.

Complete the table by writing the missing steps using register transfer notation and the missing descriptions.

Interrupts can be caused by software programs or hardware devices.

State one cause of a software interrupt.

The following statements describe the stages that the CPU performs when an interrupt is detected.

There are three missing statements.

Write the letter of the missing statements from the table in the correct place to complete the description.

1. At the end of each Fetch-Execute (F-E) cycle, the processor checks if an interrupt flag is set.
2. ...............................
3. If the interrupt priority is high enough, the processor saves the current contents of the registers.
4. .................................
5. When servicing of the interrupt is complete, the processor restores the registers.
6. ...................................

A computer has several Universal Serial Bus (USB) ports.

Identify two different peripheral devices that could be connected to this computer using a USB port.

A company buys a new printer. The printer is connected to one of the computer's Universal Serial Bus (USB) ports.

Give two benefits and one drawback of using a USB port to connect the printer.

A student buys a microphone that has a Universal Serial Bus (USB) connector. The microphone has never been connected to the student's computer before.

The student plugs the microphone into a USB port on the computer.

Explain what the computer does so that the microphone can be used.

A computer is connected to a television using a High Definition Multimedia Interface (HDMI) port.

State the two types of data that are carried by this HDMI connection.

The fetch stage of the Fetch-Execute (F-E) cycle can be written using register transfer notation.

Complete the table by writing the register transfer notation for each description.

A designer connects a computer to a monitor using an HDMI port. The monitor displays images that contain a very large number of pixels.

Explain why the HDMI connection does not reduce the quality of the image that is displayed.

A computer system is designed using the basic Von Neumann model.

Describe what is meant by the stored program concept.

A student writes two steps of the fetch stage using register transfer notation.

MAR ← [PC]

MDR ← [MAR]

The second step is written incorrectly.

Write the correct register transfer notation for the second step and explain why the student's version is wrong.

A lecture theatre has a projector with built-in speakers. The projector has both a Video Graphics Array (VGA) port and a High Definition Multimedia Interface (HDMI) port.

A laptop is connected to the projector to show a presentation that contains video clips with sound.

Explain why the HDMI port is the better choice for this connection.

A computer system is designed using the basic Von Neumann model. The components of the system are connected by an address bus, a data bus and a control bus.

Complete the table by writing the name of the bus that carries each item.

A monitor is connected to a computer using a Video Graphics Array (VGA) port.

(i) State the type of signal that is sent through a VGA port. [1]

(ii) State the type of data that a VGA port carries. [1]

A processor in a computer system needs to write a data value to a location in main memory.

Describe how the address bus, the data bus and the control bus are used to carry out this write operation.

A computer is designed using the basic Von Neumann model.

• The instruction LDD 415 is stored in memory location 300.
• Memory location 415 stores the value 62.
• At the start of a fetch stage the Program Counter (PC) stores 300.

Complete the table to show the contents of each register at the end of the fetch stage, before the instruction is decoded and executed.

A computer has a VGA port and no other port for connecting a display. It is connected by a VGA cable to a monitor that has built-in speakers.

When a video is played on the computer, the picture appears on the monitor but no sound comes from the monitor speakers.

Explain why no sound is heard, and state what the user must do so that the sound can be heard from the monitor speakers.

A Central Processing Unit (CPU) contains several special purpose registers.

State the role of each of the following registers.

Current Instruction Register (CIR)

Accumulator (ACC)

A program is running on a computer.

(i) State when, during the Fetch-Execute (F-E) cycle, the processor checks whether an interrupt has occurred.

(ii) State one cause of a hardware interrupt.

A shop uses a computer to display adverts on a screen. The screen is a long way from the computer and is connected to it using a long VGA cable.

The picture on the screen is faint and the colours are poor. When the same screen is connected to the computer using a short VGA cable, the picture is clear.

Explain why the length of the VGA cable affects the quality of the picture.

A program stores a list of values in consecutive locations in main memory. The same instruction is used repeatedly to read each value in turn.

Describe how the Index Register (IX) makes this possible.

A computer is printing a long document. The printer sends an interrupt to the processor each time its buffer becomes empty.

Explain the role of the Interrupt Service Routine (ISR) when the processor handles this interrupt.

A computer has a processor with four cores.

State what is meant by a core.

A student writes the following about two special purpose registers.

"The Memory Address Register (MAR) stores the data that has been read from main memory. The Memory Data Register (MDR) stores the address of the location that the data came from."

Identify the error in each statement and give the correct role of each register.

A weather forecasting program divides a large calculation into many separate tasks that can be carried out at the same time.

The program is moved from a computer with a single-core processor to a computer with a four-core processor of the same type.

Explain why the program is likely to run faster on the four-core processor.

A program is running on a computer. A hardware device generates an interrupt.

After the interrupt has been handled, the program must continue from exactly the point it had reached, with the values it was working on unchanged.

Explain how the processor makes this possible.

The Arithmetic and Logic Unit (ALU) is a component of the Central Processing Unit (CPU).

State two types of operation that are carried out by the Arithmetic and Logic Unit (ALU).

A company replaces its computers. The old computers have a two-core processor. The new computers have a four-core processor of the same type.

The company expects every program to run in half the time. It finds that some programs run only a little faster.

Explain why doubling the number of cores does not double the performance of the computer.

The table describes three actions that are carried out inside a Central Processing Unit (CPU).

Complete the table by writing the name of the component that carries out each action.

Do not include registers or buses in your answers.

A processor contains a system clock.

(i) State what is meant by the clock speed of a processor.

(ii) State the unit in which clock speed is measured.

A processor has its clock speed increased.

Explain how a higher clock speed allows the processor to carry out more instructions each second.

A large program is stored on a hard disk drive. When the user runs the program, the operating system copies the instructions of the program into the Immediate Access Store (IAS).

Explain why the instructions must be copied into the Immediate Access Store (IAS) before the processor can run them.

A shop sells two computers. Processor P has a higher clock speed than Processor Q. The two processors have different architectures.

A customer buys the computer with Processor P because it has the higher clock speed. The computer with Processor Q runs the customer's programs faster.

Explain why a higher clock speed does not always mean better performance.

A processor uses cache memory.

State two features of cache memory.

A computer is upgraded so that its processor has a larger amount of cache memory.

Explain how this can improve the performance of the computer.

A computer runs two programs.

Program A repeatedly carries out the same short set of instructions on a small amount of data.

Program B reads every record in a very large data file once, and does not read any record a second time.

The amount of cache memory in the computer is increased.

Explain why the performance of Program A is likely to improve more than the performance of Program B.

A computer has a data bus that is 32 bits wide.

(i) State what is meant by a data bus that is 32 bits wide.

(ii) State the effect on data transfer of increasing the width of the data bus to 64 bits.

The table shows information about two of the buses in a computer.

Complete the table.

A computer has an address bus that is 20 bits wide and a data bus that is 16 bits wide.

Each memory location stores one byte.

(i) Calculate the number of memory locations that can be directly addressed.

Show your working.

(ii) Calculate the total size of the memory that can be directly addressed.

Give your answer in mebibytes. Show your working.