DualMode Operation

I/O Protection

Hardware Address Protection

Memory Protection

CPU Protection

Speed

Cost

Volatility

Caching

Storage Device Hierarchy

Main memory

Secondary storage

Magnetic disks

Synchronous I/O Structure

Asynchronous I/O Structure

Two I/O Methods

The operating system preserves the stateof the CPU by storing registers and theprogram counter.

Determines which type of interrupt hasoccurred, either by:

Separate segments of code determinewhat action should be taken for each typeof interrupt.

Each device controller has a local buffer

The CPU and device controllers can

execute concurrently

Each device controller is in charge of aspecific type of device

CPU moves data from/to main memoryto/from local buffers

I/O is from the device to local buffer of

controller

Device controller informs CPU that it hasfinished its operation by causing aninterrupt