Previous chapters of the text describe two of the major components found in a
computer system: processors and memories. In addition to describing technologies used
for each component, the chapters illustrate how processors and memory interact.
This chapter introduces the third major aspect of architecture, connections between
a computer and the external world. We will learn that on most computers, the connection
between a processor and memory uses the same basic paradigm as the connection
between a processor and an I/O device, and we will see that although they operate
under control of a processor, I/O devices can interact directly with memory.