Memory System Design I - Fundamentals of Computer Organization and Architecture - page 107

& CHAPTER 6
Memory System Design I
In this chapter, we study the computer memory system. It was stated in Chapter 3
that without a memory no information can be stored or retrieved in a computer. It
is interesting to observe that as early as 1946 it was recognized by Burks, Goldstine,
and Von Neumann that a computer memory has to be organized in a hierarchy. In
such a hierarchy, larger and slower memories are used to supplement smaller and
faster ones. This observation has since then proven essential in constructing a com-
puter memory. If we put aside the set of CPU registers (as the first level for storing
and retrieving information inside the CPU, see Chapter 5), then a typical memory
hierarchy starts with a small, expensive, and relatively fast unit, called the cache.
The cache is followed in the hierarchy by a larger, less expensive, and relatively
slow main memory unit. Cache and main memory are built using solid-state semi-
conductor material. They are followed in the hierarchy by far larger, less expensive,
and much slower magnetic memories that consist typically of the (hard) disk and the
tape. Our deliberation in this chapter starts by discussing the characteristics and fac-
tors influencing the success of a memory hierarchy of a computer. We then direct our
attention to the design and analysis of cache memory. Discussion on the (main)
memory unit is conducted in Chapter 7. Also discussed in Chapter 7 are the
issues related to virtual memory design. A brief coverage of the different read-
only memory (ROM) implementations is also provided in Chapter 7.
6.1. BASIC CONCEPTS
In this section, we introduce a number of fundamental concepts that relate to the
memory hierarchy of a computer.
6.1.1. Memory Hierarchy
As mentioned above, a typical memory hierarchy starts with a small, expensive, and
relatively fast unit, called the cache, followed by a larger, less expensive, and rela-
tively slow main memory unit. Cache and main memory are built using solid-state