Introduction of Computer Organization and Architecture: Two Marks Important Questions and Answers

Computer Organization and Architecture

Chapter 1: Introduction

 

Two Marks Questions with Answers

 

1. Define computer architecture.

Answer: Computer architecture is defined as the functional operation of the individual H/W unit in a computer system and the flow of information among the control of those units.

2. Define computer H/W.

Answer: Computer H/W is the electronic circuit and electro mechanical equipment that constitutes the computer.

3. Name the functional units of a computer.

Answer: The functional units of a computer are:

1. Input unit

2. Output unit

3. Control unit

4. Memory unit

5. Arithmetic and logical unit.

4. What is meant by Central Processing Unit (CPU)?

Answer: The arithmetic and logic unit in conjunction with control unit is commonly called Central Processing Unit (CPU).

5. What is the function of input unit ?

Answer: A computer accepts a digitally coded information through input unit using input devices such as keyboard and mouse.

6. What are the functions of control unit?

Answer: The control unit co‒ordinates and controls the activities amongst the functional units. The basic function of control unit is to fetch the instructions stored in the main memory, identify the operations and the devices involved in it and accordingly generate control signals to execute the desired operations.

7. What is the function of arithmetic and logic unit ?

Answer: The Arithmetic and Logic Unit (ALU) is responsible for performing arithmetic operations such as add, subtract, division and multiplication and logical operations such as ANDing, ORing, inverting etc.

8. What is the role of MAR and MDR ?

Answer: The MAR (memory address register) is used to hold the address of the location to or from which data are to be transferred and the MDR(memory data register) contains the data to be written into or read out of the addressed location.

9. What is the role of IR ?

Answer: Instruction Register (IR) contains the instruction being executed. Its output is available to the control circuits, which generate the timing signals for controlling the processing circuits needed to execute the instructions.

10. What is the role of PC ?

Answer: The Program Counter (PC) register keeps track of the execution of the program. It contains the memory address of the instruction currently being executed. During the execution of the current instruction, the contents of the PC are updated to correspond to the address of the next instructions to be executed.

11. What is an interrupt?

Answer: An interrupt is an event that causes the execution of one program to be suspended and another program to be executed.

12. What are the uses of interrupts ?

Answer:

1. Recovery from errors

2. Debugging

3. Communication between programs

4. Use of interrupts in operating system.

13. What do you mean by alignment restriction?

Answer:

• In MIPS, the registers are 32‒bit; hence, the word size is 32‒bit (4 bytes).

• Since most memories are byte (8‒bits) oriented, virtually all architectures today address individual bytes. However, the byte should be the starting byte of the word.

• Therefore, in MIPS, words must start at addresses that are multiples of 4. This requirement is called an alignment restriction and many architectures have it.

14. Why are the most frequently used variables stored in registers ?

Answer: Registers take less time to access and have higher throughput than memory. Hence, the compiler tries to keep the most frequently used variables in registers.

15. What is spilling registers ?

Answer: The process of putting less commonly used variables (or those needed later) into memory is called spilling registers.

16. List various logical operations supported by MIPS.

Shift Left, Shift Right, AND, OR and NOT Operations

17. List the decision making instructions supported by MIPS assembly language.

AND, OR and NOT Operations

18. What is instruction set architecture?

Answer: One of the most important abstraction is the interface between the hardware and the lowest‒ level software. Because of its importance, it is given a special name: The instruction set architecture of a computer. It includes anything programmer needs to know to make a binary machine language program work correctly, including instructions, I/O devices and so on.

19. What are the various types of operations required for instructions ?

Answer:

• Data transfers between the main memory and the CPU registers

• Arithmetic and logic operation on data

• Program sequencing and control

• I/O transfers.

20. What is operation code ?

Answer: The operation code field in the instruction specifies the operation to be performed. The operation is specified by binary code, hence the name operation code or simply opcode.

21. What are addressing modes ?

Answer: The different ways that a processor can access data are referred to as addressing schemes or addressing modes.

22. List different addressing modes.

Answer:

1. Register mode

2. Absolute mode or direct mode

3. Immediate mode

4. Indirect mode

5. Index mode

6. Relative mode

7. Autoincrement mode

8. Autodecrement mode.

23. Differentiate direct and indirect addressing mode.

Answer: In direct addressing mode the address of the location of the operand is given explicitly as a part of the instruction. On the other hand, in indirect addressing mode, the effective address of the operand is the contents of a register or the main memory location whose address is given explicitly in the instruction.

24. State the need for indirect addressing mode. Give an example.

Answer: In indirect addressing mode, the instruction specifies the address where the address of the operand is located. In case of register indirect addressing, the address of the operand is specified by the contents of the register. These operating modes are needed when we need to access arrays. Specifically, in register indirect addressing, registers are used as pointers and they are very useful for dealing with arrays or tables of simple data values.

Fig. 1.14.1 Register indirect addressing

Consider Fig. 1.14.1, where a data structure consists of a sequence of consecutive byte values. The pointer register contains (1000)н, corresponding to the first item in the structure. To access item 2 in the structure we only need to increment the value in the pointer register.

25. What is CISC architecture ?

Answer: CISC (Complex Instruction Set Computer) architecture uses a large set of complex instructions, where each instruction can perform multiple low‒level operations, such as memory access, arithmetic and logic, in a single instruction.

26. What is RISC architecture ?

Answer: RISC (Reduced Instruction Set Computer) architecture uses a small and simple set of instructions, each designed to execute very quickly, usually within one clock cycle.

27. Give one example each of CISC and RISC processors.

Answer:

• CISC processor: Intel x86 family

• RISC processor : ARM, MIPS, or PowerPC

28. State one main difference between CISC and RISC.

Answer: CISC has many complex instructions that may take multiple cycles to execute, while RISC

has fewer and simpler instructions that typically execute in one clock cycle.

29. State the basic addressing modes supported by RISC processor.

Answer: The RISC processor has three basic addressing modes:

• Register addressing

• Immediate operand and

• Relative to PC addressing for branch instructions.

30. What is assembly language?

Answer: Assembly language is a symbolic form of machine language that uses mnemonics (like add, sub, lw) instead of binary numbers, making programming easier for humans.

31. What is the role of an assembler ?

Answer: An assembler translates assembly language code into machine language (binary instructions) that the computer can execute.

32. What are the two main sections of a MIPS program?

Answer:

• Data Section (.data): Declares variables and constants.

• Text Section (.text) : Contains executable instructions (program code).

33. Define pseudo‒instruction with an example.

Answer: Pseudo‒instructions are assembler‒provided instructions that make coding easier but are not real hardware instructions.

Example:

move $t1, $t2 → translated to add $t1, $t2, $zero.

34. What is the difference between a real instruction and a pseudo‒instruction?

Answer: A real instruction is directly executed by hardware, while a pseudo‒instruction is expanded by the assembler into one or more real MIPS instructions.

35. What are the three steps of translating a program from high‒level language to machine code?

Answer:

1. High‒Level Language → written by humans (e.g., sum = a + b;)

2. Assembly Language → symbolic form (add $t0, $t1, $t2)

3. Machine Language → binary code executed by hardware

36. What is the function of a compiler ?

Answer: A compiler translates high‒level language code into assembly language or machine language for execution.

37. What is a benchmark?

Answer: A benchmark is a standard program used to measure and compare the performance of different computer systems.

38. What is the purpose of SPEC benchmarks ?

Answer: SPEC benchmarks provide standardized tests to evaluate CPU performance and energy efficiency across different systems.

39. Differentiate between CINT2006 and CFP2006.

Answer:

• CINT2006: Measures performance of integer‒based programs (e.g., compiling, simulations).

• CFP2006: Measures floating‒point performance (e.g., scientific or engineering applications).

40. What is SPECratio and what does it indicate ?

Answer: SPECratio = Execution time on reference system / Execution time on test system.

A higher SPECratio means better (faster) performance.

41. What does SPEC Power benchmark measure ?

Answer: It measures a server's energy efficiency ‒ the performance achieved per watt of power consumed at different load levels.

42. Why did the industry shift from uniprocessors to multiprocessors ?

Answer: Because increasing clock speed caused high power consumption and heat generation. Multicore processors improved performance through parallelism instead.

43. What is a multicore processor?

Answer: A multicore processor is a single chip containing two or more independent processing cores that can execute instructions simultaneously.

44. State any two advantages of multicore processors.

Answer:

1. Higher throughput (more work done per unit time).

2. Ability to execute multiple programs or tasks in parallel.

45. What is parallelism in computer systems ?

Answer: Parallelism means performing multiple operations simultaneously to increase computational speed and efficiency.

46. Mention different levels of parallelism.

Answer:

• Instruction‒level parallelism (ILP)

• Data‒level parallelism (DLP)

• Thread‒level or task‒level parallelism (TLP)

47. What are the main challenges in parallel programming?

Answer: Scheduling, Load balancing, Synchronization and Communication overhead.

48. What is cache coherence ?

Answer: Cache coherence ensures that all processor cores in a multicore system have the most recent copy of shared data in their caches.

49. What is the function of synchronization instructions?

Answer: They help coordinate multiple tasks by accessing shared data, preventing conflicts or race conditions.

50. What is the role of GPUs in parallel computing ?

Answer: GPUs perform thousands of operations simultaneously, making them ideal for data‒parallel tasks like AI, image processing, and simulations.

51. What is subword parallelism?

Answer: Subword parallelism allows a single instruction to perform operations on multiple smaller data elements simultaneously, improving performance in multimedia and scientific applications.

52. What is RAID and why was it developed ?

Answer: RAID (Redundant Array of Inexpensive Disks) combines multiple disks to increase I/O throughput and improve data reliability through parallel access.