1.1. consists of one / more CPUs and a number of device controllers
1.2. Each device controller has a local buffer
1.3. The CPU & device controller can execute concurrently
2. Asynchronous I/O Structure
2.1. System call
2.2. Device
3. Interrupt handling
3.1. When the CPU interrupted, it stops immediately
3.2. Interrupt vector provide the address of the interrupt service routine for the interrupt service routine for the interrupting devices
4. I/O Protection
4.1. User program must executes a system call to request that the OS to perform I/O
5. Dual mode operation
5.1. in order to ensure the proper execution of the operating system the computer must be able to distinguish bw the execution of OS code & user-defined code
6. Storage Hierarchy
6.1. Speed
6.2. cost
6.3. volatility
7. Storage Structure
7.1. Main memory
7.2. Secondary storage
8. Synchronous I/O Structure
8.1. wait instruction idles the CPU until the next interrupt
8.2. wait loop
8.3. At most one I/O request is outstanding at a fine, no simultaneous I/O processing.
