1. Basic Computer Architecture Models

The 5 Component Model

A computer system can be divided into 5 components:
  1. Hardware
  2. Software
  3. Data
  4. Procedures
  5. Personnel

In studying Computer Systems' Architecture, only the first 3 of these are of direct interest.




One of the major requirements of any computer system is the ability to represent and manipulate values ("data").

In general, digital computers (the only type considered in this course) represent values as patterns of "off" and "on" signals. Each value requires a different pattern (or, at least, a pattern which is different from any other value of the same type). Different types of values generally are represented using different "encoding schemes". An "encoding scheme" specifies how many "off" and "on" signals are required for each value, and provides a unique pattern of signals for each possible value.

Data vs. Information

Two terms common in any discussion of computer systems are "data" and "information". The difference in meaning between these two terms is based on the concept that "information" is "data" which has "meaning" to someone (or something) outside of the computer system.

"Information" is "data" which has meaning. The most common task of a computer system (especially when the input source and the output destination are the same) is to transform data into information. In fact, this is sometimes used as the basis for alternative definitions of a computer system .

The concept of "meaning" can be difficult. Generally, we think of "meaning" as implying that something with intelligence exists for which the "data" has meaning. When the output of a computer system is the automated control of some other system (as in CAD, Computer Aided Manufacturing), we end up debating, the unresolved question of what is meant by "intelligence".

1. The IPO(S) Model

A computer system can be thought of as a collection of components which together are capable of 3 operations: Input, Processing, and Output. A fourth operation, Storage, is also required for practical computer systems.

Note that the IPO(S), Input-Process-Output(-Storage), model is applied to at least two different areas:

  1. the collection of "equipment" that makes up a computer system
  2. the "actions" that a computer system is capable of performing.


A computer system must include a method for accepting "data" and "instructions" from outside the system.

Power or energy sources required to enable operation of the computer system are not "inputs".


A computer system must include the ability to change or "transform" data which has been input. These "transformations" typically include (but are not limited to)


A computer system must include the ability to send processed data to outside the system in a form that can be used by the "outside world". This "outside world" might be the human "users" of the computer system, but alternatively could be electrical or mechanical controls for automated equipment, or the "inputs" for some other system.


We would not normally consider a collection to be a computer system unless it included some form of memory of previous input or processed data. For example, system composed of an electrical power supply, an on/off switch, a light bulb, and appropriate wiring to connect the other three components would not normally be considered to be a computer system (although it contains IPO elements of a basic form). Replacing the on/off switch with a "toggle button", which would reverse the current on/off "state" of the light, would give us something closer to a computer system.

For the purposes of this course memory (or "storage") will be considered to be an essential element of any computer system.