Introduction to Models - Introduction to Computer Science - Lecture Slides, Slides of Computer Science

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Introduction

to Models

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 Define the Turing model of a computer.

 Define the von Neumann model of a computer.

 Describe the three components of a computer: hardware, data, and software.

 List topics related to computer hardware.

 List topics related to data.

 List topics related to software.

 Discuss some social and ethical issues related to the use of computers.

 Give a short history of computers.

Objectives

After studying this chapter, the student should be able to:

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Data processors

Before discussing the Turing model, let us define a computer as a data processor. Using this definition, a computer acts as a black box that accepts input data, processes the data, and creates output data (Figure 1.1). Although this model can define the functionality of a computer today, it is too general. In this model, a pocket calculator is also a computer (which it is, in a literal sense).

Figure 1.1 A single purpose computing machine

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Programmable data processors

The Turing model is a better model for a general-purpose computer. This model adds an extra element to the specific computing machine: the program. A program is a set of instructions that tells the computer what to do with data. Figure 1.2 shows the Turing model.

Figure 1.2 A computer based on the Turing model

• Figure 1.4 The same data, different programs Docsity.com 1.

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The universal Turing machine

A universal Turing machine , a machine that can do any computation if the appropriate program is provided, was the first description of a modern computer. It can be proved that a very powerful computer and a universal Turing machine can compute the same thing. We need only provide the data and the program—the description of how to do the computation—to either machine. In fact, a universal Turing machine is capable of computing anything that is computable.

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Computers built on the von Neumann model divide the computer hardware into four subsystems: memory , arithmetic logic unit , control unit , and input/output (Figure 1.5).

Four subsystems

Figure 1.5 The von Neumann model

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The von Neumann model states that the program must be stored in memory. This is totally different from the architecture of early computers in which only the data was stored in memory: the programs for their task was implemented by manipulating a set of switches or by changing the wiring system.

The memory of modern computers hosts both a program and its corresponding data. This implies that both the data and programs should have the same format, because they are stored in memory. In fact, they are stored as binary patterns in memory— a sequence of 0s and 1s.

The stored program concept

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1-3 COMPUTER COMPONENTS

We can think of a computer as being made up of three components: computer hardware , data , and computer software.

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Computer hardware today has four components under the von Neumann model, although we can have different types of memory, different types of input/output subsystems, and so on. We discuss computer hardware in more detail in Chapter 5.

Computer hardware

The von Neumann model clearly defines a computer as a data processing machine that accepts the input data, processes it, and outputs the result.

Data

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Figure 1.6 Program and data in memory

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Figure 1.7 A program made of instructions

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Mechanical machines (before 1930)

During this period, several computing machines were invented that bear little resemblance to the modern concept of a computer.

 In the 17th century, Blaise Pascal, a French mathematician and philosopher, invented Pascaline.

 In the late 17th century, a German mathematician called Gottfried

Leibnitz invented what is known as Leibnitz’ Wheel.

The first machine that used the idea of storage and programming was the Jacquard loom , invented by Joseph-Marie Jacquard at the beginning of the 19 th^ century.

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 In 1823, Charles Babbage invented the Difference Engine. Later, he invented a machine called the Analytical Engine that parallels the idea of modern computers.

 In 1890, Herman Hollerith , working at the US Census Bureau, designed and built a programmer machine that could automatically read, tally, and sort data stored on punched cards.