Hardware Reference
In-Depth Information
2
COMPUTER SYSTEMS
ORGANIZATION
A digital computer consists of an interconnected system of processors, memo-
ries, and input/output devices. This chapter is an introduction to these three com-
ponents and to their interconnection, as background for a more detailed examina-
tion of the specific levels in the five subsequent chapters. Processors, memories,
and input/output are key concepts and will be present at every level, so we will
start our study of computer architecture by looking at all three in turn.
2.1 PROCESSORS
The organization of a simple bus-oriented computer is shown in Fig. 2-1. The
CPU ( Central Processing Unit ) is the ''brain'' of the computer. Its function is to
execute programs stored in the main memory by fetching their instructions, exam-
ining them, and then executing them one after another. The components are con-
nected by a bus , which is a collection of parallel wires for transmitting address,
data, and control signals. Buses can be external to the CPU, connecting it to mem-
ory and I/O devices, but also internal to the CPU, as we will see shortly. Modern
computers have multiple buses.
The CPU is composed of several distinct parts. The control unit is responsible
for fetching instructions from main memory and determining their type. The arith-
metic logic unit performs operations such as addition and Boolean AND needed to
carry out the instructions.
55
 
 
 
Search WWH ::




Custom Search