1.
1 Organization and Architecture
Computer architecture: refers to those attributes of a
system visible to a programmer or, put another way, those
attributes that have a direct impact on the logical
execution of a program. Examples of architectural
attributes include the instruction set, the number of bits
used to represent various data types (e.g., numbers,
characters), I/O mechanisms, and techniques for
addressing memory.
refers to the operational units and their
interconnections that realize the architectural
specifications. Organizational attributes
include those hardware details transparent to
the programmer, such as control signals;
interfaces between the computer and
peripherals; and the memory technology
used.
A computer is a complex system; contemporary computers
contain millions of elementary electronic components.
How, then, can one clearly describe them?
The key is to recognize the hierarchical nature of most
complex systems, including the computer. A hierarchical
system is a set of interrelated subsystems, each of the
latter, in turn, hierarchical in structure until we reach some
lowest level of elementary subsystem.
The hierarchical nature of complex systems is essential to
both their design and their description. The designer need
only deal with a particular level of the system at a time. At
each level, the system consists of a set of components and
their interrelationships.
The behavior at each level depends only on a simplified,
abstracted characterization of the system at the next lower
level. At each level, the designer is concerned with
structure and function:
Structure: The way in which the components
are interrelated
Function: The operation of each individual
component as part of the structure
In terms of description, we have two choices:
starting at the bottom and building up to a
complete description, or beginning with a top
view and decomposing the system into its
subparts. Evidence from a number of fields
suggests that the top down approach is the
clearest and most effective.
the simplest possible depiction of a computer
Data Processing
The computer, of course, must be able to process
data. The data may take a wide variety of forms,
and the range of processing requirements is broad.
However, we shall see that there are only a few
fundamental methods or types of data processing.
Data Storage
It is also essential that a computer store data. Even
if the computer is processing data on the fly (i.e.,
data come in and get processed, and the results go
out immediately), the computer must temporarily
store at least those pieces of data that are being
worked on at any given moment. Thus, there is at
least a short-term data storage function. Equally
important, the computer performs a long-term
data storage function. Files of data are stored on
the computer for subsequent retrieval and update.
Move Data
The computer must be able to move data between itself
and the outside world. The computer’s operating
environment consists of devices that serve as either
sources or destinations of data. When data are received
from or delivered to a device that is directly connected to
the computer, the process is known as input–output (I/O),
and the device is referred to as a peripheral. When data are
moved over longer distances, to or from a remote device,
the process is known as data communications.
Control
Finally, there must be control of these three functions.
Ultimately, this control is exercised by the individual(s)
who provides the computer with instructions. Within the
computer, a control unit manages the computer’s
resources and orchestrates the performance of its
functional parts in response to those instructions.
