Other components must know how to interact with bus. Abstractions for accessing devices routines for low-level device operations. Provide equitable access to shared resources. Memory system ignores those addresses. Device controller sees the operation and performs accordingly.
Devices typically have one or more status registers used for communication.
May include done bit and one or more types of error bits. Polling process of periodically checking status bits. Device sets bits, processor checks. O Used by almost all systems for at least some devices. O interrupts to tell processor that a device needs attention.