Computer Architecture and Organization CAT

 

1. Define Computer Architecture (2 marks)

Computer architecture refers to the design and organization of the various components of a computer system, including the central processing unit (CPU), memory, input/output devices, and buses, as well as the way these components interact with one another to execute instructions and process data efficiently.

2. Explain the different types of memory hierarchy in a computer system. (3 marks)

The memory hierarchy in a computer system refers to the arrangement of various types of memory based on their speed, size, and cost. It is structured as follows:

• Registers: The fastest memory located inside the CPU, used to store small amounts of data that are immediately required for processing.
• Cache Memory: A small, fast memory located between the CPU and main memory, used to store frequently accessed data to speed up processing.
• Main Memory (RAM): Volatile memory that stores data and instructions currently being used by the CPU.
• Secondary Storage: Non-volatile memory like hard drives or SSDs, used to store data persistently.

Each level in the hierarchy balances speed, size, and cost to optimize overall system performance.

3. What is Instruction Cycle? Describe its different phases. (4 marks)

The Instruction Cycle is the process by which the CPU fetches, decodes, and executes instructions. It consists of several phases:

1. Fetch: The CPU retrieves the next instruction from memory, based on the address stored in the Program Counter (PC).
2. Decode: The fetched instruction is decoded by the Control Unit to determine the operation to be performed.
3. Execute: The decoded instruction is executed, which could involve performing arithmetic operations, moving data, or interacting with I/O devices.
4. Store: The result of the execution may be stored in registers or memory.

This cycle repeats for each instruction in a program.

4. Discuss the different types of buses in a computer system and their functions. (5 marks)

Buses are communication pathways that transfer data between different components of a computer system. There are three main types of buses:

• Data Bus: Carries data between the CPU, memory, and I/O devices. It is bidirectional, allowing data transfer in both directions.
• Address Bus: Carries memory addresses from the CPU to the memory or I/O devices, determining the location to read from or write to. It is unidirectional.
• Control Bus: Carries control signals from the CPU to other components to manage operations, like read/write signals, interrupt requests, and clock signals.

Together, these buses enable data flow and coordination in a computer system.

5. What is Memory Addressing? (2 marks)

Memory addressing refers to the method used by the CPU to access specific locations in memory. It involves assigning unique addresses to each memory location, allowing the CPU to retrieve or store data from a particular address. The two main types of addressing are direct addressing (where the memory address is specified directly) and indirect addressing (where the address points to another address). 

6. What is the difference between RISC (Reduced Instruction Set Computer) and CISC (Complex Instruction Set Computer) architectures? (4 marks)

The primary differences between RISC and CISC architectures are:

• RISC (Reduced Instruction Set Computer):

  • Uses a small set of simple instructions.
  • Each instruction is typically executed in one clock cycle.
  • Emphasizes software optimization.
  • More instructions may be needed for complex tasks, but it is highly efficient in pipeline execution.

• CISC (Complex Instruction Set Computer):

  • Uses a large set of complex instructions.
  • Instructions can execute multiple operations in a single cycle.
  • Emphasizes hardware optimization to handle more complex tasks in fewer instructions.
  • The CPU is more complex due to the variety of instructions. 

7. Explain the purpose of cache memory and how it improves system performance. (4 marks)

Cache memory is a small, high-speed memory located between the CPU and main memory. Its purpose is to store frequently accessed data or instructions to reduce the time the CPU spends waiting for data from slower main memory.

It improves system performance by:

• Reducing Access Time: Cache memory is much faster than main memory, allowing the CPU to quickly retrieve data.
• Decreasing Latency: By storing recently or frequently used data, it reduces the time needed to fetch data from slower memory.
• Increasing Overall Speed: With data available in the cache, the CPU can process instructions more quickly, improving overall system performance.

8. What are Registers, and how do they differ from main memory? (2 marks)

Registers are small, fast storage locations within the CPU used to hold data that is immediately needed for processing. They differ from main memory (RAM) in the following ways:

• Size: Registers are much smaller in size compared to main memory.
• Speed: Registers are faster than main memory.
• Purpose: Registers store temporary data during computation, while main memory stores data and instructions that are actively used by the CPU.

9. Define microprocessor and explain its role in a computer system. (2 marks)

A microprocessor is the central processing unit (CPU) of a computer on a single integrated circuit (IC) chip. It performs the basic functions of a computer system, including executing instructions, performing calculations, and managing data flow between components. It serves as the brain of the computer, carrying out the instruction cycle and controlling all other hardware components.

10. What is the function of the Program Counter (PC) in a CPU? (2 marks)

The Program Counter (PC) is a register in the CPU that holds the memory address of the next instruction to be executed. After each instruction is fetched, the PC is incremented to point to the subsequent instruction in memory, ensuring that the CPU executes the program in the correct sequence.