Device Management and Input/Output

Objectives :

• Provide a uniform and simple view of I/O (hide complexity of device handling)
• Provide device independence from : device type - terminal, disk or tape, device instance : which terminal, which tape etc
• Fair access to shared devices
• Smooth allocation of dedicated devices
• Important : Ability to exploit parallelism of I/O devices for multiprogramming

Devices can however vary considerably :

• Differences in speed, synchronous or asynchronous
• Unit of data transfer - character or block
• Character codes - are they all the same ? Does everyone use the same representation
• Operations supported : read, write, seek, print etc
• Error Conditions
• Sharable or is it only for a single user (e.g. printer, tape, kettle ?)