Subject: Operating Systems

Topic: Input Output Management

Difficulty: High

Application I/O Interface represents the structuring techniques and interfaces for the operating system to enable I/O devices to be treated in a standard, uniform way. The actual differences lies kernel level modules called device drivers which are custom tailored to corresponding devices but show one of the standard interfaces to applications. The purpose of the device-driver layer is to hide the differences among device controllers from the I/O subsystem of the kernel, such as the I/O system calls.

Following are the characteristics of I/O interfaces with respected to devices:

• Character-stream / block - A character-stream device transfers bytes in one by one fashion, whereas a block device transfers a complete unit of bytes.

• Sequential / random-access - A sequential device transfers data in a fixed order determined by the device, random access device can be instructed to seek position to any of the available data storage locations.

• Synchronous / asynchronous - A synchronous device performs data transfers with known response time where as an asynchronous device shows irregular or unpredictable response time.

• Sharable / dedicated - A sharable device can be used concurrently by several processes or threads but a dedicated device cannot be used.

• Speed of operation - Device speeds may range from a few bytes per second to a few gigabytes per second.

• Read-write, read only, or write only - Some devices perform both input and output, but others support only one data direction that is read only.