Question

(a) Describe the three fundamental ways for performing I/O and compare their advantages and disadvantages. b) A hard disk rotates at 15,000 rpm and has 1024 tracks, each with 2048 sectors. It takes 100 ms for the head to cross 1024 racks. Assume that the head is above the innermost track. i. What is the average seek time? ii. What is the average rotational delay (latency)? iii. What is the transfer time for one sector? You can round the result to the nearest microsecond. iv. Using the above results compute the total average time to service a request of reading 1024 consecutive sectors. You can round the result to the nearest millisecond.

Answer 1

a.

I/O systems:

In Operating systems management of I/O devices plays very important role and entire all I/O subsystems are devoted and run under its operation.For example we take modern computer and its parts like keyboards, disk drives, display adapters, USB devices, audio I/O, printers, network connections and other -purpose peripherals.

I/O subsystems has two types of trends.

1. For wide range of devices it is easy to add newly developed devices to an existing systems .
2. For these types the existing standard interfaces ane difficult and not easy to apply for the development of entirely new types of devices.

Device frivers are nothig b ut modules and these are plugged in to an Operatinf system to handler .

1.I/O hardware:

I/O devices can be roughly categorized as storage, communications, user-interface, and other
Devices communicate with the computer via signals sent over wires or through the air.
Devices connect with the computer via ports, e.g. a serial or parallel port.
A common set of wires connecting multiple devices is termed a bus.

We can say that I/O devices are commonly defined as storage, user-interface, communications and other sets.Coming to devices these will communicate with the computer via the signals . These signals will sent over through the air and over some wires.Some devices will connect to the computer via ports.We know that we have a serial port and parallel port. The same set of wires if they connected to multiple devices known as    BUS.

Polling

Polling will be very fast and efficient when only both the device and controller are fast and had a efficient and significant data to transfer.However sometimes it become inefficient when the host waits longtime in the loop which is in busy waiting for the device or if the infrequent will happen if the frequent checks will not me made.

Application I/O Interface

while application layers are presented with a common interface for all devices through layering user applications will access to a number of diffrent devices is possible and using through encapsulating all the device specific codes are in to device drivers.

B.

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