Tài liệu Memory Architecture

6.1 Chapter Overview
This chapter discusses the memory hierarchy – the different types and performance levels of memory
found on a typical 80x86 computer system. Many programmers tend to view memory as this big nebulous
block of storage that holds values for future use. From a semantic point of view, this is a reasonable view.
However, from a performance point of view there are many different kinds of memory and using the wrong
one or using one form improperly can have a dramatically negative impact on the performance of a program.
This chapter discusses the memory hierarchy and how to best use it within your programs.
6.2 The Memory Hierarchy
Most modern programs can benefit greatly from a large amount of very fast memory. A physical reality,
however, is that as a memory device gets larger, it tends to get slower. For example, cache memories (see
“Cache Memory” on page 153) are very fast but are also small and expensive. Main memory is inexpensive
and large, but is slow (requiring wait states, see “Wait States” on page 151). The memory hierarchy is a
mechanism of comparing the cost and performance of the various places we can store data and instructions.
Figure 6.1 provides a look at one possible form of the memory hierarchy.