coa unit v 2marks

8/7/2019 Coa Unit v 2marks

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UNIT V- I/O ORGANIZATION

1.what are the various mechanisms for implemernting I/O operations?

Program controlled I/O

Interrupts

DMA

2.what are vectored interrupts?

To reduce the time involved in the polling process,a device requesting an interrupt mayidentify itself directly to the processor.Then the ,processor can immediately start executing the

corresponding ISR.The schemes based on this approach is called vectored interrupts.

3. when the privilege exception arises?An attempt to execute a privileged instruction while in the user mode leads to a special type of

interrupt called a privilege exception.

4.what are the 2 independent mechanisms for controlling interrupt request? At the device end,an interrupt enable bit in a control register determines whether

the device is allowed to generate an interrupt request. At the processor end,either an interrupt enable bit in the PS or a priority structure

determines whether a given interrupt request will be accepted.

5.what is time slicing?With this technique each program runs for a short period called a time slice.

6.What is cycle stealing?The processor originates most memory access cycles and the DMA controller can be said

to stael memory cyckles from the processor.This technique is known as cycle stealing.

7.what are the three types of buses?

Address bus Data bus

Control bus

8. Why IO devices cannot be directly be connected to the system bus?Ans: The IO devices cannot be directly connected to the system bus because

i. The data transfer rate of IO devices is slower that of CPU.

ii. The IO devices in computer system has different data formats and

work lengths that of CPU.

So it is necessary to use a module between system bus and IO device called IO moduleor IO system

9. What are the major functions of IO system?Ans: i. Interface to the CPU and memory through the system bus.

ii. Interface to one or more IO devices by tailored data link.10. What is an I/O Interface?

Ans: Input-output interface provides a method for transferring binary informationbetween internal

storage, such as memory and CPU registers, and external I/O devices

11. Write the factors considered in designing an I/O subsystem?


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Ans:

1. Data Location: Device selection, address of data with in device(track, sector etc)

2. Data transfer: Amount, rate to or from device.

3. Synchronization: Output only when device is ready, input only when

4.Memory or between an I/O device and CPU.

12. Explain Direct Memory Access.

Ans: * A modest increase in hardware enables an IO device to transfer a block ofinformation to orfrom memory without CPU intervention. This task requires the IOdevice to generate memory

addresses and transfer data through the bus using interfacecontrollers.

y Transfer of a block of data directly between an external device and main memory, without continuous intervention by the processor is called DMA.

13. Define DMA controller.

Ans: The I/O device interface control circuit that is used for direct memory access isknown as DMA

controller.

DMA transfers are performed by a control circuit that is part of the I?O device

interface.This cuircuit is known as DMA controller.

14. What is polling?Ans: Polling is a scheme or an algorithm to identify the devices interrupting theprocessor. Polling is

employed when multiple devices interrupt the processor through one interrupt pin of the processor.

15. What is the need of interrupt controller?

Ans: The interrupt controller is employed to expand the interrupt inputs. It can handlethe interruptrequests from various devices and allow one by one to the processor.

16.What is a Priority Interrupt?Ans: A priority interrupt is an interrupt that establishes a priority

over the various sources to determine which condition is to be serviced first when two or morerequestsarrive simultaneously.

17. Define bus.

Ans: When a word of data is transferred between units, all the bits are transferred inparallel over a

set of lines called bus. In addition to the lines that carry the data, the busmust have lines for address

and control purposes.

18. Define synchronous bus. Ans: Synchronous buses are the ones in which each item is transferred

during a timeslot(clock cycle) known to both the source and destination units. Synchronization can

be achieved by connecting both units to a common clock source.

In this, all devices derive timing information from a common clock line.

19. Define asynchronous bus.

Ans: Asynchronous buses are the ones in which each item being transferred is accompanied by acontrol signal that indicates its presence to the destination unit. The destination can respond with

another control signal to acknowledge receipt of the items.In this, all devices do not derive timing information from a common clock line. It uses

handshake between the master and the slave.

20. What do you mean by memory mapped I/O?Ans: In Memory mapped I/O, there are no specific input or output instructions. The CPU can

manipulate I/O data residing in interface registers with the same instructions that are used tomanipulate memory words .


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When the I/O devices share the same address space, the arrangement is called memory

mapped I/O.

21. What is program-controlled I/O?

Ans: In program controlled I/O the processor repeatedly checks a status flags to achieve the

required synchronization between the processor and an input and output device.

22. Define interrupt.Ans: An interrupt is any exceptional event that causes a CPUU to temporarily transfer control from

its current program to another program , an interrupt handler that services the event in question.

23. Define exception.Ans: The term exception is used to refer to any event that causes an interruption

24. What are the different methods used for handling the situation when multiple interrupts

occurs?Ans: 1) Vectores interrupts

2) Interrupt nesting

3) Simultaneous Requests.25. What is a privileged instruction?Ans: To protect the operating system of a computer from being corrupted by user programs, certain

instructions can be executed only while the processor is in the supervisor mode. These are called

privileged instruction.

26. What is bus arbitration?Ans: it is process by which the next device to become the bus master is selected and busmastership

is transferred to it. There are two ways for doing this:

1. Centralized arbitration

2. Distributed arbitration.27. What is port? What are the types of port available?Ans: An I/O interface consists of circuitry required to connect an I/O device tocomputer bus. One

side consists of a data path with its associated controls to transferdata between the interface and I/Odevice. This is called port. It is classified into:

1) Parallel port2) Serial port.

28. What is a parallel port?

Ans: A parallel port transfers data in the form a number of bits, typically 8 to 16,simultaneously to

or from the device.

29. What is a serial port?Ans: A serial port transfers and receives data one bit at a time.

30. What is PCI bus?Ans: The Peripheral component interconnect(PCI) bus is a standard that supports theany particular

processor.

31. What is SCSI?Ans: It is the acronym for small computer system interface. It refers to a standard busdefined ANSI.

Devices such as disks are connected to a computer via 50-wire cable,which can be upto 25 meters in


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length and can transfer data at rate up to 55megabytes/s.

32. Define USB.Ans: The Universal Serial Bus(USB) is an industry standard developed to provide twospeed of

operation called low-speed and full-speed. They provide simple, low cost andeasy to use

interconnection system.

33.What are the objectives of USB? Simple

Low cost Easy to use

Supports wide range of data transfer characteristics. Plug and play mode of operation

Part A (2Marks)

1. What are the functions of I/O interface?

2. How does the processor handle an interrupt request?

3. What are the necessary operations needed to start an I/O operation using DMA?

4. What are the three types of channel usually found in large computers?

5. Why does a DMA have priority over the CPU when both request a memory transfer?

6. What is the advantage of using interrupt initiated data transfer?

7. Why do you need DMA?

8. What is the difference between subroutine and interrupt service routine?

9. What is the need for interrupt masks?

10. How does bus arbitration typically works?

11. How does a processor handle an interrupt?

12. Distinguish synchronous bus and asynchronous bus.

13. Why I/O devices cannot be directly be connected to the system bus?

14. What are the major functions of I/O system?

15. What is an I/O interface?16. Write the factors considered in designing an I/O subsystem?

17. Explain Direct Memory Access.

18. Define DMA controller.

19. What is polling?

20. What is the need of Interrupt controller?

21. What is a priority interrupt?

22. Define bus.

23. Define synchronous bus.

24. Define asynchronous bus.

25. State the differences between memory mapped I/O and I/O mapped I/O.

26. Define interrupt.27. Define exception.

28. What are the different methods used for handling the situation when multiple

interrupts

occurs?

29. What is a privileged instruction?

30. What is bus arbitration?

31. What is port? What are the types of port available?

32. What is a parallel port?


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33. What is a serial port?

34. What is PCI bus?

35. What is SCSI?

36. Define USB.

Part B

1. Explain the functions to be performed by a typical I/O interface with a typical input

output

interface.(16)

2. Discuss the DMA driven data transfer technique.(8)

3. Discuss the operation of any two input devices(8)

4. Explain in detail about interrupt handling.(16)

5. Explain in detail about standard I/O interface.(16)

6. Describe the functions of SCSI with a neat diagram.(16)

7. What is the importance of I/O interface? Compare the features of SCSI and PCI

interfaces.(8)

8. Write note on the following.

a) Bus arbitration b) Printer process communication

c) USB

d) DMA(16)

9. Explain the use of vectored interrupts in processes. Why is priority handling desired in

interrupt controllers? How does the different priority scheme work?(8)

10. Explain with the detail of I/O devices.

11.Expian the Following

1.PCI

2.SCSI

3.USB

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