LEARNING OBJECTIVES
After studying this chapter, you should be able to:
Present an overview of the main characteristics of computer memory systems
Describe the basic concepts and intent of cache memory.
Discuss the key elements of cache design.
Distinguish among direct mapping, associative mapping, and set-associative
Explain the reasons for using multiple levels of cache.
Understand the performance implications of multiple levels of memory.
Although seemingly simple in concept, computer memory exhibits perhaps the wid-
est range of type, technology, organization, performance, and cost of any feature
of a computer system. No single technology is optimal in satisfying the memory
requirements for a computer system. As a consequence, the typical computer
system is equipped with a hierarchy of memory subsystems, some internal to the
system (directly accessible by the processor) and some external (accessible by the
processor via an I/O module).
is devoted to external memory. To begin, the first section examines key characteristics
of computer memories. The remainder of the chapter examines an essential element
of all modern computer systems: cache memory.
4.1 COMPUTER MEMORY SYSTEM OVERVIEW
and the use of a memory hierarchy.
mapping.
This chapter and the next focus on internal memory elements, while Chapter 6