UNIT I - PART A Questions

UNIT - I  COMPUTER ORGANIZATION & INSTRUCTIONS

2-MARK QUESTIONS AND ANSWERS

1.    List the eight great ideas invented by computer architects. (May 2015)

The eight great ideas in computer architecture are:

1.    Design for Moore’s Law

2.    Use Abstraction to Simplify Design

3.    Make the Common (frequent) Case Fast

4.    Performance via Parallelism

5.    Performance via pipelining

6.    Performance via Prediction

7.    Hierarchy of Memories

8.    Dependability via Redundancy

2.     State Amdahl’s law.                                                                (Nov – 2014)

     Amdahl’s law states that the performance enhancement possible with a given improvement is limited by the amount that the improved feature is used.

Amdahl’s law defines speedup and it is given by

Speedup = Performance for entire task using the enhancement when possible  

                   Performance for entire task without using the enhancement             

3.    Brief about relative addressing mode with an example.     (Nov – 2014)

     Here the referenced register is program counter (PC) and hence this addressing mode is also known as PC-relative addressing mode.

     In PC-addressing mode the branch address is calculated by the sum of the PC value and a constant in the instruction.

      EX: beq $s1, $s2, 200

4.    Define Response Time.

     Response time is also called execution time.  The total time required for the computer to complete a task, including disc accesses, memory accesses, I/O activities, operating system overhead, CPU execution time, and so on is called response time.

5.    Define Throughput

Throughput or bandwidth is the total amount of work done in a given time.

6.    Define Addressing Modes

     The different ways in which the operands of an instruction are specified are called as addressing modes.  The MIPS addressing are the following:

·         Immediate addressing

·         Register addressing

·         Base or displacement addressing

·         PC – relative addressing

·         Pseudo direct addressing

7.    What are the MIPS instruction format types?

I-   Format

R- Format

J- Format

8.    What is a compiler?

     The system software program called a compiler translates the high-level language program into a suitable machine language program containing instruction such as the Add and Load instructions.

9.    What is elapsed time of computer system?

     The total time to execute the total program is called elapsed time.  It is affected by the speed of the processor, the disk and the printer.

10. What is big endian and little endian format?

The name big endian is used when lower byte addresses are specified in the most significant bytes (MSB) of the word.  The name little endian is used when lower byte addresses are specified in the least significant bytes (LSB)  of the word.

11. What is text editor?

     It is used for entering and editing application programs.  The user of this program interactively executes command that allow statements of a source program entered at a keyboard to be accumulated in a file.

12. Define Application Binary Interface (ABI)

     The user portion of the instruction set plus the operating system interfaces used by application programmers is called as application binary interface.

13. What is multiprogramming?

     The operating system manages the concurrent execution of several application programs to make the best possible uses of computer resources.  This type of concurrent execution is called multiprogramming.

14. Distinguish pipelining from parallelism.

     The pipelining breaks a big task into number of small parts. A part higher in order gets processed and serves as an input for the next sub-task, while in parallel processing various tasks are run at the same time. Pipelining processing deals with N-client single server whereas parallel support N-client N-server.

15. Define Stored Program concepts.

      Today’s computers are built on two key principles.

·         Instructions are represented as numbers.

·         Programs are stored in memory to be read or written, just like data.

     These principles lead to the stored-program concept.  Treating instructions in the same way as data greatly simplifies both the memory hardware and the software of computer systems.

16. What are the fields in an MIPS instruction?

MIPS fields are

Op		rs	rt	rd		shamt		funct
6 bits	5 bits		5 bits		5 bits		5 bits		6bits

Where

Op : Basic operation of the instruction, traditionally called the opcode.

rs :  The first register source operand.

rt  :  The second register source operand.

rd :   The register destination operand. It gets the result of the operation.

shamt :  Shift amount.

funct :  Funcition.

17. Define MIPS.

Million instructions Per Second (MIPS) is a measurement of program execution speed based on the number of millions of instruction.  MIPS is computed as :

      MIPS = Instruction count /   (Execution time x 10⁶)

18. Write the formula for CPU clock cycles required for a program.

CPU clock cycles = Number of Instructions in a program x Average clock cycles per instruction.

19. Write the formula for CPU execution time for a program.

CPU execution time       = for a program	Number of CPU clock cycles for a program x Clock cycles time
Alternatively because clock rate and clock cycle time are inverses,
CPU execution time   = for a program	CPU clock cycles for a program / Clock rate

20. What are the basic components of performance?

Components of performance	Units of measure
CPU execution time for a program	Measured in seconds
Instruction count	Number of instructions in the program
Clock cycles per instruction (CPI)	Average number of clock cycles per instruction
Clock cycle time	Time for one clock cycle in seconds

21. If computer A runs a program in 10 seconds, and computer B runs the same program in 15 seconds, how much faster is A over B.

We know that A is n times faster than B if

Performance e_A / Perfromance e_B =    Execution time _B  / Execution time _A     

Thus the performance ratio is

15/10 = 1.5

and A is therefore 1.5 times faster than B.

22. State the need for indirect addressing mode.  Give an example. Need for indirect addressing mode.                                                              (Apr / May 2017)

     In base register addressing (or) indirect addressing, we add a small constant to a pointer held in a register.  The register may point a structure or some other collection of data, and we need to load a value at a constant offset from the beginning of the structure.  Because each MIPS instruction fits in one word, the size of the constant is limited to 16 bits.

23. Brief about Relative addressing mode with an example.            (Nov / Dec 2014)

     In PC – relative addressing mode, the branch address is the sum of the PC and a constant in the instruction.  Program Counter (PC) contains the address of the current instruction.

24. What is an instruction register?

     An Instruction register (IR) is the part of a CPU’s control unit that holds the instruction currently being executed or decoded. In simple processors each instruction to be executed is loaded into the instruction register which holds it while it is decoded, prepared and ultimately executed, which can take several steps.

25. What are the components of a computer?

Hardware component

·         Input unit

·         Memory unit

·         Arithmetic and Logic Unit

·         Output unit

·         Control unit

Software component

·         System Software

·         Application software.

    

26. Define Moore’s law.

Integrated circuit resources double every 18-