Input-Output Device

Input-Output Device

• I/O devices are divided into three types: Human readable, Machine readable and Communication.

1. Human readable

• Computer user can communicate with computer using human readable device. These devices are help to user for giving input to computer and reading result.

• Example: Printer, display, keyboard and mouse.

2. Machine readable

• Machine readable is used for communicating with electronic devices and components.

• Example: USB device, disk drivers, controller, sensors etc.

3. Communication

• This type I/O devices used for communicating with remote devices.

• Example: modem, digital line drivers

• I/O devices are differentiating on following parameters.

1. Data rate

2. Application used

3. Complexity of control

4. Error conditions

5. Data representation

6. Unit of transfer

1. Data rate: will change according to the input output devices. There may be differences of several orders of magnitude between the data transfer rates. Data transfer rate of keyboard is the lowest among the entire I/O device.

2. Application used: Different devices have different use in the system.

3. Complexity of control: It will change according to the input-output devices. Printer requires a relatively simple control interface. Disk is much more complex interface.

4. Error conditions: The nature of errors differ widely from one device to another.

5. Data representation: Different data encoding schemes are used for different devices.

6. Unit of transfer: Data may be transferred as a stream of bytes or characters or in larger blocks.

Example 5.6.1 Why is it important to balance file-system I/O among the disks and controllers on a system in a multitasking environment?

Solution: A system can perform only at the speed of its slowest bottle-neck. Disks or disk controllers are frequently the bottleneck in modern systems as their individual performance cannot keep up with that of the CPU and system bus. By balancing I/O among disks and controllers, neither an individual disk nor a controller is overwhelmed, so that bottleneck is avoided.