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Chapter 5 Internal Memory
The design of a main memory system is a never-ending battle among
three competing design requirements: large storage capacity, rapid access
time, and low cost. As memory technology evolves, each of these three
characteristics is changing, so that the design decisions in organizing main
memory must be revisited anew with each new implementation. Chapter
5 focuses on design issues related to internal memory. First, the nature
and organization of semiconductor main memory is examined. Then,
recent advanced DRAM memory organizations are explored.

Chapter 6 External Memory
For truly large storage capacity and for more permanent storage than is
available with main memory, an external memory organization is needed.
The most widely used type of external memory is magnetic disk, and
much of Chapter 6 concentrates on this topic. First, we look at magnetic
disk technology and design considerations. Then, we look at the use of
RAID organization to improve disk memory performance. Chapter 6 also
examines optical and tape storage.

Chapter 7 Input/Output
I/O modules are interconnected with the processor and main memory, and
each controls one or more external devices. Chapter 7 is devoted to the var-
ious aspects of I/O organization.This is a complex area, and less well under-
stood than other areas of computer system design in terms of meeting
performance demands. Chapter 7 examines the mechanisms by which an
I/O module interacts with the rest of the computer system, using the tech-
niques of programmed I/O,interrupt I/O,and direct memory access (DMA).
The interface between an I/O module and external devices is also described.

Chapter 8 Operating System Support
A detailed examination of operating systems (OSs) is beyond the scope
of this book. However, it is important to understand the basic functions of
an operating system and how the OS exploits hardware to provide the de-
sired performance. Chapter 8 describes the basic principles of operating
systems and discusses the specific design features in the computer hard-
ware intended to provide support for the operating system. The chapter
begins with a brief history, which serves to identify the major types of op-
erating systems and to motivate their use. Next, multiprogramming is ex-
plained by examining the long-term and short-term scheduling functions.
Finally, an examination of memory management includes a discussion of
segmentation, paging, and virtual memory.

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