Computer Architecture-2 Marks Question and Answers

PART A

1.Define Computer Architecture

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

  Computer H/W Is The Electronic Circuit And Electro Mechanical Equipment That Constitutes The Computer

3. What Is Meant By Cache Memory ?

A Memory That Is Smaller And Faster Than Main Memory And That Is Interposed Between The Cpu And Main Memory. The Cache Acts As A Buffer For Recently Used Memory Location

4.what is locality of reference?

Many instruction in localized area of the program are executed repeatedly during some time period and the remainder of the program is accessed relatively infrequently .this is referred as locality of reference.

5.what is IO mapped input output? OR What is isolated I/O?,What is I/O Mapped I/O?

A memory reference instruction activated the READ M (or)WRITE M control line and does not affect the IO device. Separate IO instruction are required to activate the READ IOand WRITE IO lines ,which cause a word to be transferred between the address aio port and the CPU. The memory and IO address space are kept separate.

6.specify the three types of the DMA transfer techniques?

Single transfer mode(cyclestealing mode)

Block Transfer Mode(Brust Mode)

Demand Transfer Mode

Cascade Mode

7. why is memory refreshing circuit needed ?

al cells on the corresponding yow to be read and refreshed during both read and write operation .the contents of the d ram are maintained each row of cell must be accessed periodically once every 2 – 16 ms.  refresh circuit usually performs this function .

automatically

8 what are the functions of control unit ?

the memory  arithmetic and logic ,and input   and output units store and process information and perform i/p and o/p operation, the operation of these unit must be co ordinate in some way this  is the task of control unit the cu is effectively the nerve center  that sends the control signal to other units and sence their states.

9.What is an interrupt?

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

10.What are the uses of interrupts?

• Recovery from errors
• Debugging
• Communication between programs
• Use of interrupts in operating system

11.Define vectored interrupts.

  In order to reduce the overhead involved in the polling process, a device requesting an interrupt may identify itself directly to the CPU. Then, the CPU can immediately start executing the corresponding interrupt-service routine. The term vectored interrupts refers to all interrupt-handling schemes base on this approach.

12. What is the need for reduced instruction chip?

1.      Relatively few instruction types and addressing modes.

2.      Fixed and easily decoded instruction formats.

3.      Fast single-cycle instruction execution.

4.      Hardwired rather than microprogrammed control.

13. Name any three of the standard I/O interface.

1.      SCSI (small computer system interface),bus standards

2.      Back plane bus standards

3.      IEEE 796 bus (multibus signals)

4.      NUBUS

5.      IEEE 488 bus standard

14. Differentiate between RISC and CISC

RISC                                                                            CISC

1.      Reduced Instruction  Set Computer                     1. Complex Instruction set computer

2.      Simple instructions take one cycle per                 2. Complex instruction take multiple

Operation.                                                                  Cycles per operation.

3.      Few instructions and address modes are              3. Many instruction and address   

Used.                                                                         Modes.

4. Fixed format instructions are used.                        4. Variable format instructions are

                                                                                             used.

5.Instructions are compiled and then                          5. Instructions are interpreted by the   

   executed by hardware.                                                 Microprogram and then executed.

6.  RISC machines are multiple register                     6. CISC machines use single register

set.                                                                             Set.

7.  Complexity in the compiler                                   7. Complexity in the microprogram

8. RISC machines are higly piplined                          8. CISC machines are not piplined.

15.Explain the pipeline types.

1. Instruction pipeline
2. Arithmetic pipeline

16. Explain the various classifications of parallel structures.

1.      SISD (single instruction stream single data stream

2.      SIMD(single instruction stream multiple data stream

3.      MIMD(multiple instruction stream multiple data stream

4.      MISD(multiple instruction stream single data stream

17. What is absolute addressing mode?

   The address of the location of the operand is given explicitly as a part of the instruction.

 Eg. Move a , 2000

18. Specify three types of data transfer techniques.

1.      Arithmetic data transfer

2.      Logical data transfer

3.      Programmed control data transfer

19. What is the role of MAR and MDR?

  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.

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

1.      Data transfers between the main memory and the CPU registers

2.      Arithmetic and logic operation on data

3.      Program sequencing and control

4.      I/O transfers

21. What is the role of IR and PC?

  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.

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.

22.Define memory access time?

  The time that elapses between the initiation of  an operation and completion of that  operation ,for example ,the time between the READ  and the MFC signals .This is

Referred  to as memory access time.   

23. Define memory cycle time.

     The minimum time delay required between the initiations of two successive memory operations, for example, the time between two successive READ operations.

24.Define Static Memories.

   Memories that consist of circuits capable of retaining the state as long as power is applied are known as static memories.

25.Distinguish Between Static RAM and Dynamic RAM?

Static RAM are fast, but they come at high cost because their cells require several transistors. Less expensive RAM can be implemented if simpler cells are used. However such cells do not retain their state indefinitely; Hence they are called Dynamic RAM.

26.Distiguish between asynchronies DRAM and synchronous RAM.

  The specialized memory controller circuit provides the necessary control signals, RAS And CAS ,that govern the timing. The processor must take into account the delay in the response of the memory. Such memories are referred to as asynchronous DRAMS.

The DRAM whose operations is directly synchronized with a clock signal. Such

Memories are known as synchronous DRAM

 

27.what are the various units in the computer?

   1,input unit

   2.output unit

   3.control unit

   4.memory unit

5.arithmetic and logical unit

28.what is an I/O channel?

  An i/o channel is actually a special purpose processor, also called peripheral processor.

The main processor initiates a transfer by passing the required information in the input output channel. the channel then takes over and controls the actual transfer of data.

29.what is a bus?

   A collection of wires that connects several devices is called a bus.

30.Define word length?

     Each group of n bits is referred to as a word of information and n is called the word length.

31.explain the following the address instruction?

  1.three-address instruction-it can be represented as

        add a,b,c

       Operands a,b are called source operand and c is called destination operand.

2.two-address instruction-it can be represented as

        add a,b

3.one address instruction-it can be represented as

   add a

4.1 1/2 address instruction

   it can be represented the type of instruction in which one address always refers to a location in the main memory and the other, shorter address always refers to a cpu register, is intermediate to the one-two-address formats because of this property is called I ½ address  format.

5.zero address instruction.

   It is also possible to use instruction where the location s of all operand are defined implicitly. This operand of the use of the method for storing the operand in which  called push  down stack. Such instructions are sometimes referred to us zero address instruction.

32.what is the straight-line sequencing?

       the  cpu control circuitry automatically proceed to fetch and execute instruction, one at a time in the order of the increasing addresses. This is called straight line sequencing.

33.what is the role of pc?

     The cpu contains a register called the program counter, which holds the address of instruction to be executed next.. to begin the execution of the program the address of its

First instruction must be placed into the pc.

34.what are steps for execution of a complete instruction?

  1.fetch the instruction.
   2.fetch the first operand (the contents of the memory location pointed by the address field of the instruction.)

3.perform the calculation.

4.load the result.

35.what is a a  bit slice?

   A bit slice is “slice” through the data path of the typical processor. It contains all

Circuits necessary to provide alu function, register transfer and control function for only a few bits of the data path.

36.what is DMA?

 

          A special control unit may be provided to enable transfer a block of data directly between an external device and memory without contiguous intervention by the cpu. This approach is called DMA.

37.why program controlled I/O is unsuitable for high-speed data transfer?

1. in program controlled i/o considerable overhead is incurred.. because several program instruction have to be executed for each data word  transferred between the external devices and MM.
2. many high speed peripheral; devices have a synchronous modes of operation.

that is  data transfer are controlled by a clock of fixed frequency, independent of the cpu.

38.what is the function of i/o interface?

      The function is to coordinate the transfer of data between the cpu and external devices.

39.what is NUBUS?

     A NUBUS  is a processor independent, synchronous bus standard intended for use in

32 bit micro processor system. It defines a backplane into which upto 16 devices may be plugged each in the form of circuit board of standard dimensions.

40. what do you mean associative mapping technique?

  The tag of an address received from the CPU is compared to the tag bits of each block of the cache to see if the desired block is present. This is called associative mapping technique.

41. What is LRU replacement algorithm?

   When a block is to be overwritten it is sensible to overwrite the one that has gone the largest time without being referenced. This block is called Least Recently Used block  and the technique is called LRU replacement algorithm.

42. Explain virtual memory technique.

     Techniques that automatically move program and data blocks into the physical memory when they are required for execution are called virtual memory technique.

43. What are virtual and logical addresses?

      The binary addresses that the processor issues for either instruction or data are called virtual or logical addresses.

44. Define translation buffer.

        Most commercial virtual memory systems incorporate a mechanism that can avoid the bulk of the main memory access called for by the virtual to physical addresses translation buffer. This may be done with a cache memory called a translation buffer, which retains the results of the recent translation.

45. Name some of the IO devices.

                                                            1.            Video terminals

                                                            2.            Video displays

                                                            3.            Alphanumeric displays

                                                            4.            Graphics displays

                                                            5.            Flat panel displays

                                                            6.            Printers

                                                            7.            Plotters

46. What is branch delay slot?

     The location containing an instruction that may be fetched and then discarded because of the branch is called branch delay slot.

47. What is optical memory?

        Optical or light based techniques for data storage, such memories usually employ optical disk which resemble magnetic disk in that they store binary information in concentric tracks on an electromechanically rotated disks. The information is read as or written optically, however with a laser replacing the read write arm of a magnetic disk drive. Optical memory offer high storage capacities but their access rate is are generally less than those of magnetic disk.

48. What is microprogrammed control?

      Microprogrammed control in which control signals are generated by a program similar to machine language program. A sequence of one (or) more microoperation, such as addition, multiplication is called a micro program. The address where these microinstructions are stored in CM is generated by microprogrammed control.

49. What is microprogramming?

      A sequence of Control Words corresponding to the control sequence of a machine instruction constitutes the micro routine for that instruction, and the individual control words in this micro routine are referred to as microinstructions.

       Microprogramming is a method of control unit design in which the control signal selection and sequencing information is stored in a ROM (or) RAM called a control memory CM.

50.What are static and dynamic memories?

   Static memory are memories which require periodic no refreshing. Dynamic memories are memories, which require periodic refreshing.

51. What are the steps required for a pipelinened processor to process the instruction?

1.      F Fetch: read the instruction from the memory

2.      D   Decode: decode the instruction and fetch the source operand(s).

3.      E   Execute: perform the operation specified by the instruction.

4.      W   Write: store the result in the destination location.

52. What are the steps taken when an interrupt occurs?

1.      Source of the interrupt

2.      The memory address of the required ISP

3.      The program counter & cpu information saved in subroutine

4.      Transfer control back to the interrupted program

53 Define instruction pipeline.

   The transfer of instructions through various stages of the cpu instruction cycle., including fetch opcode,decode opcode,compute operand addresses. Fetch operands, execute instructions and store results. This amounts to realizing most (or) all of the cpu in the form of multifunction pipeline called an instruction pipelining.

54. Define latency.

        The term memory latency is used to refer to the amount of time it takes to transfer  a word of data to or from the memory. The term latency is used to denote the time it takes to transfer the first word of data. This time is usually substantially longer than the time needed to transfer each subsequent word of a block.

55. Define bandwidth.

        Bandwidth is a product of the rate at which the data are transferred (and accessed) and the width of the data bus.

56. Define hit rate.

      A successful access to data in a cache is called a hit. Number of hits stated as a fraction of all attempted accesses is called the hit rate.

57. Define miss rate.

       A miss rate is the number of misses stated as a fraction of attempted accesses. Extra time needed to bring the desired information into the cache is called the miss penalty.

58. Distinguish between system space and user space.

            assembling the operating system routine into a virtual address space , is called system space that is separate from the virtual space in which user application program reside. The latter space is called user space.

59.Define

1. Signal  - The binary information is represented in digital computers by physical quantities called signals.

3. Gates – The manipulation of binary information is done by logic circuits called gates. Gates are blocks of hardware that produce signals of binary 1 or 0 where input logic requirements are satisfied.

3. Flip flop – The storage elements employed in clocked sequential circuits are called flip flops. A flip flop is a binary cell capable of storing 1 bit of information.

60. Define combinational circuit.

            A combinational circuit is a connected arrangement of logic gates with the set of inputs and outputs. A combinational circuit transforms binary information from the given input data to the required output data. Combinational are employed in digital computers required for generating binary control decisions and for providing digital components required for data processing.

61. Define sequential circuits.

A sequential circuit is an interconnectin of flip-flops and gates. The gates by themselves constitute a combinational circuit, but when included with the flip flops, the overall circuit is classified as a sequential circuit.

62.    Define interface.

          The word interface refers to the boundary between two circuits or devices.

 

63.    Define pipelining.

Pipelining is a techinique of decomposing a sequential process into sub operations with each subprocess being executed in a special dedicated segment that operates concurrently with all other segments.

64.    Define parallel processing.

Parallel processing is a term used to denote a large class of techniques that are used to provide simultaneous data-processing tasks for the purpose of increasing the computational speed of a computer system. Instead of processing each instruction sequentially as in a conventional computer, a parallel processing system is able to perform concurrent data processing to achieve faster execution time.

65.    What are the components of memory management unit?

1. A facility for dynamic storage relocation that maps logical memory references into physical memory addresses.

2 A provision for sharing common programs stored in memory by different users .

.3. Protection of information against unauthorized access between users and preventing users from changing operating system functions.

66.    What is programmed I/O?

          Data transfer to and from peripherals may be handled using this mode. Programmed I/O operations are the result of I/O instructions written in the computer program.

67.   Define  Memory interleaving ?

In Memory interleaving, memory is divided into several modules and the technique is used to address the memory modules in order to have reduced complexity in mapping hardware