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1 Computers and processors: introduction

Computers have become a vital part of everyday life. It is almost inconceivable that you could spend a day without at least one event being influenced by a computer. Perhaps the word ‘computer’ automatically conjures up the image of a personal computer sitting on a desk, but in fact it is the computers you cannot see that influence your life the most. Typical examples of common products that may use these ‘invisible’ computers are:

  • cars


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Learning outcomes

After studying this course, you should be able to:

  • understand what all the terms highlighted in bold in the text mean

  • understand the fundamental hardware components that make up a computer’s hardware and the role of each of these components

  • understand the difference between an operating system and an application program, and what each is used for in a computer

  • describe some examples of computers and state the effect that the use of
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References

[1] E. Freeman, S. Hupfer and A.K. Arnald, JavaSpaces Principles, Patterns and Practice. Reading, MA: Addison-Wesley, 1999.
[2] G. Coulouris, J. Dollimore and T. Kindberg, Distributed Systems Concepts and Design. Harlow: Addison-Wesley, 2001.
[3] N. Lynch, Distributed Algorithms. New York: Morgan Kauffman, 1996.
[4
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Conclusion

This free course provided an introduction to studying Computing and ICT. It took you through a series of exercises designed to develop your approach to study and learning at a distance and helped to improve your confidence as an independent learner. 


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5.2 An example

In order to complete this section I shall present a simple example. This is loosely based on one described in [1], currently one of the very few books written on JavaSpaces technology.

An object that can be stored in a space has to implement an interface Author(s): The Open University

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4.3 A commercial implementation

In order to conclude this section I shall describe a commercial implementation of an object bus. It has been developed by a company known as SoftWired Ltd and is known as iBus. It is based on TCP/IP rather than UDP. The facilities offered by the iBus API provide developers with the facilities to construct objects which can subscribe to channels and to transmit any Java object to a channel. The code for a transmitter is shown below; the import statements are not shown. In
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1 Distributed models

Before looking in detail at some of the technologies it is worth examining some of the implementation and design models that can be used for distributed system development ranging from the familiar, message passing, to the unfamiliar, tuple-based technology. In describing these I have two aims: first, to detail the variety of methods and architectures that are available and the degree of closeness they have to Internet technologies such as TCP/IP, for example message passing is close in conce
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6.1 What is a business model?

The aim of this section is to look at some of the business models which have been used to drive internet applications. A business model is a high-level description of an application type which contains all the common features which can be found in specific examples of the model. For example, one of the most popular business models is the e-shop which describes a website that sells products. The model is general in that it does not describe the item that is sold or the mechanisms that a
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5.4 The Sydney Olympic Games system

IBM was responsible for the computer systems which were used in the 2000 Olympic Games. There were a number of components to the system, these included:

  • A website which was publicly accessible and which contained features on the Games, the competitors and the results.

  • A Games management system which administered the logistics of the Games, for example arranging transportation, accreditation and accommodation for athletes.


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5.1 The architecture of a typical e-commerce system

Before finishing this course it is worth looking at the architecture of a typical e-commerce system in order to see some of the technologies. This is followed by details of a real application which I shall use to discuss some of the issues involved in distributed system development. The description used is closely modelled on the Amazon site.


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4.7 Design

Designing a distributed system can also be a problem, for example the fact that computers in a distributed system are joined by communication media which can stretch over thousands of miles provides an added dimension to the design process in that response time can be a problem. Another, equally serious problem is that of reliability, for example the fact that a hardware malfunction can bring down a poorly-designed distributed system.

As an example of one design problem that a distribut
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4.6 Problems with transactions

A distributed transaction is a sequence of operations applied to a number of distributed databases which form a single functional step. For example, a transaction which moves an amount of money from a customer's account to an account owned by the same customer is an example of a transaction. It consists of two operations: the operation of debiting one account and the operation of crediting another account. There are a number of problems associated with distributed transactions. This section w
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4.5 Structure and data

A problem that is being increasingly experienced by internet companies is the fact that they have to interchange a large amount of data and that such data inherently lacks structure. For example, HTML has proved to be an enduring markup language for developing web pages; however, there are no facilities within the language, for example, to indicate whether an item of data, say a three-digit number, represents the price of a commodity or some hourly rate charged by a company employee.

Th
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4.4 The speed of development

E-commerce consultants speak of a web year. This is the time which it takes to bring to implementation a conventional system that would normally take a calendar year to develop. Current estimates are that one calendar year is equivalent to seven web years. Nowhere is there more of an imperative for companies to develop products and services quickly, together with the computing infrastructure required to support them, than in e-commerce. In software engineering terms this has given rise to a n
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4.3 Programming and abstraction

In the early 1990s programming an application for the internet was a tough proposition. I remember that I once had an application which required a very simple form of communication with another application located at a remote computer. I used a technology known as Winsocks which required me to carry out some pretty arcane code development just to send a simple test message to another computer and to receive a reply from that computer.

Java, when it appeared in 1996, enabled developers t
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4.2 Security and privacy

The internet is not a particularly secure place. There are two aspects to this: the first is that information is widely published throughout the internet which can be used for criminal and near-criminal activities. The second aspect is that since the internet is an open system, details of its underlying technologies are freely available to anybody. This means that the way data passes through the internet is in the public domain; the consequence of this is that, theoretically, anyone with the
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4.1.3 No dynamic web pages

Another example of a problem with web servers which arises from their original functionality is the fact that web pages were designed to be static: they were files which were stored on a computer and delivered in their stored form to anyone using a browser to access them. Many e-commerce and e-business applications require something much more dynamic, for example there are a number of financial service sites on the web which provide customers with up-to-date stock and share prices. These pric
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4.1.2 Stateless servers

Web servers are what are known as stateless servers. What this means is that in their pure form they keep no memory of what has previously happened to them between requests; for example, when a request is processed by a web server for a page they have no direct knowledge about whether the page request was made by the same browser that asked for a previous page to be returned.

While this was not serious when web servers were being mainly used for dispensing documentation (their or
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4.1.1 Space problems

Probably the best known of these is the fact that the internet is running out of space for identifying computers. Each computer in a network needs to be identified by a unique data pattern known as an IP address. The current technology used to transport data around the internet is such that in the comparatively near future we shall run out of space to hold these unique addresses. Happily this is a problem that has been identified and groups of researchers around the globe have developed new t
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4.1 Legacy technology

The aim of Section 5 is to examine some of the issues and problems which affect the devekopment of Internet, e-commerce and e-business applications.

The World Wide Web was developed as a way of dispensing documentation within the large research laboratory at CERN in Geneva. I am sure that the originator of the technology, Tim Berners-Lee, did not realise at that stage how it would expand and become a major component of our economic infrastructure. Because many of the developers o
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