Question

There are three computers and every computer has a printer connected to it. assume that the first system uses programmed i/o, the second uses interrupt and the third is based on dma. design the i/o interface for these three computer systems and printer. compare the performance of the different i/o modes for this device (printer).

Answer 1

      Computer usefulness ultimately depends on its Input/Output (I/O) capabilities

·         I/O are computing facilities to provide user input/output, data storage and retrieval, and network access capabilities in the computer system

·         I/O requires specialized hardware and software facilities

·         There are 4 types of I/O devices:

o        Input                                               e.g. keyboard

o        Output                                           e.g. screen

o        Both input and output e.g. network

o        Storage                                          e.g. disk (since it is performed as I/O operation)

·         One of the most important characteristics of an I/O device is its data rate

o        Amount of data that can be transferred from/to the I/O device in a period of time

·         Data rate is typically measured as bytes or bits per second

·         I/O devices varies in their data rates and their data traffic types

·         Figure 8.1 in page 207, shows typical data rates for various I/O devices:

o        As slow as 100 of bytes per second for the keyboard

o        As fast as 100’s of MB per second in case of the network

·         There are 4 types of traffic behaviors that I/O devices may exhibit

o        Character at a time

o        Block of characters at a time

o        Burst traffic

o        Steady traffic

·         The following are the main factors that determines the data rate of an I/O device:

o        Physical limitation of the device

o        Bandwidth of the interface that interconnects the device with the CPU and memory

o        Expected data traffic on the device (e.g. keyboard does not need to have high data rate)

·         An I/O device data rate may constitute a bottleneck in the overall performance of the computer system

·         Critical I/O devices (e.g. disk, network, screen) are usually targeted for data rate enhancements