IGCSE CS Chapter 3

Which of the following are the type of bus used in the von Neumann Architecture.

• Address Bus

• Data Bus

• Control Bus

• School Bus

Answer explanation

In von Neumann Architecture, the Address Bus carries memory addresses, the Data Bus transfers actual data, and the Control Bus manages signals for coordination. The School Bus is not relevant in this context.

Which register stores the current instructions being decoded and executed?

• CIR - Current Instruction Register

• MAR - Memory Address Register

• MDR - Memory data register

• PC - Program counter

Answer explanation

The Current Instruction Register (CIR) holds the instruction currently being decoded and executed by the CPU. It is essential for the instruction cycle, making it the correct choice for this question.

Which register stores the address of the memory location currently being read from/written to?

• CIR - Current Instruction Register

• MAR - Memory Address Register

• MDR - Memory data register

• PC - Program counter

Answer explanation

The Memory Address Register (MAR) stores the address of the memory location currently being accessed. It is essential for reading from or writing to memory, making it the correct choice for this question.

Which register stores data which has just been read from memory/data and is about to be written to memory?

• CIR - Current Instruction Register

• MAR - Memory Address Register

• MDR - Memory data register

• PC - Program counter

Answer explanation

The MDR (Memory Data Register) stores data that has just been read from memory and is about to be written to memory. It acts as a buffer between the CPU and memory, making it essential for data transfer.

Which register stores the address where the next instruction to be read can be found?

• CIR - Current Instruction Register

• MAR - Memory Address Register

• MDR - Memory data register

• PC - Program counter

Answer explanation

The Program Counter (PC) is the register that holds the address of the next instruction to be executed. It increments after each instruction fetch, ensuring the CPU knows where to find the subsequent instruction.

What is clock cycle in the CPU?

• Measured in GHz, it is how fast the clock sends signals to keep computer operations in sync.

• • Measured in Mbps, which determines the speed of data transfer across the network.

• • Measured in MBps, which represents the speed of memory access in a computer.

• • Measured in Hz, which reflects the electrical frequency of a computer’s power supply.

Answer explanation

The correct answer states that a clock cycle in the CPU is measured in GHz, indicating how quickly the clock sends signals to synchronize computer operations, which is essential for processing tasks efficiently.

What is the meaning of cache in the CPU?

• A temporary memory location using dynamic RAM to store data that is permanently saved to the hard drive.

• A permanent storage location using static RAM to store the operating system and key software files.

• A temporary memory location using flash memory to store data that is rarely accessed by the processor.

• A temporary memory location using RAM to hold data/instructions that are frequently used by the processor;

Answer explanation

Cache in the CPU is a temporary memory location that uses RAM to store frequently accessed data and instructions, allowing for faster processing compared to retrieving data from slower main memory or storage.

What is a potential risk of increasing the clock speed of a CPU?

• The CPU will shut down after reaching maximum performance

• Operations may become unsynchronized, leading to overheating

• The processor's cache memory will stop functioning

• The CPU will require less power to operate

Answer explanation

Increasing CPU clock speed can lead to operations becoming unsynchronized, which may cause overheating due to excessive heat generation. This is a significant risk as it can damage the CPU.

How can adding more cores to a CPU improve performance?

• By allowing the processor to perform more tasks simultaneously

• By increasing the clock speed of each individual core

• By reducing the need for cache memory

• By decreasing the power consumption of the CPU

Answer explanation

Adding more cores to a CPU allows it to handle multiple tasks at the same time, improving overall performance. This parallel processing capability is essential for multitasking and running complex applications efficiently.

Why doesn’t doubling the number of CPU cores necessarily double performance?

• Each core uses different clock speeds

• The CPU's cooling system is not designed for multiple cores

• The CPU needs to communicate with each core, which reduces performance

• More cores require more memory, slowing down processing

Answer explanation

Doubling CPU cores doesn't guarantee double performance because the CPU must manage communication between cores. This overhead can limit the efficiency gained from additional cores, making performance improvements less than expected.