Computer Science 35 IB
Presentation
Topic 2.3 - Computer Systems
by Patrick Wong
2.3.1 Single-Tasking,
Multi-Tasking, Single-Users, and Multi-Users
2.3.2 Comparison of the Characteristics and
Applications of Different Computers
2.3.3 Definitions for a Network
2.3.4 Principles of Networking
2.3.5 Benefits of Sharing in a Network
2.3.6 Comparison Between the Benefits and Limits
of LANs and WANs
2.3.7 Applications and Implications of
Networking for Organizations
2.3.8 Web Browsers and Search Engines
2.3.9 Batch Processing, On-line (Interactive)
Processing, and Real-Time Processing
2.3.11 Master and Transaction Files
Presentation Links:
These are links to other sections in my presentation.
Online Java Computer Systems Quiz
Complete presentation in Adobe Acrobat PDF format.
Note: The PDF format of this presentation includes a bibliography, quiz, quiz key, assignment, and a handout. The quiz is slightly different from the online version.
2.3.1 Single-Tasking, Multi-Tasking, Single-Users, and
Multi-Users
Terminology:
single-tasking environments - environments (this usually refers to operating systems) that run in a mode of operation where only one program can be in use at any time. An example of a single-tasking environment is MS-DOS which only allows one program to run at a time.
multi-tasking environments - environments (this usually refers to operating systems) that run in a mode of operation that provides for concurrent performance, or interleaved execution, of two or more tasks. An example of a multi-tasking environment is Windows which allows more than one program to run at a time.
single-user systems - a system in which one user monopolizes all facilities. Eg. Portable Computer.
multi-user system - a system which can be used by two or more people to access the services of a processor within a given period of time. Eg. Mainframe
(IB Computer Science Syllabus, 2000, p.60-75)
2.3.2 Comparison of the Characteristics and Applications of
Different Computers
Personal Computer (PC) - This type of computer is usually classified as a microcomputer. Initially, personal computers were designed to be single-user systems, but more recently there have been some exceptions to this generalization. As their name implies, PCs are usually used by individuals for their own personal use but they are often used in businesses as well. A personal computer is small enough to fit on a table and they are affordable for individuals. PCs have less primary and backup storage than minicomputers or mainframes but most new PCs currently have storage capacities of 10GB or more. Common output devices for PCs are monitors and printers while common input devices are keyboards and mice. Today's PC processors are 32-bit or speeds beyond 1000MHz both of which are increasing rapidly.
Portable Computer - This type of computer is similar to a personal computer but smaller. Portable computers are classified as microcomputers and are also known as notebook computers or lab-top computers. They are usually designed to be single-user systems. Portable computers are generally used by many of the same users of PCs for similar purposes such as for personal use or business. However, the main reason users buy portable computers because they are easily portable for traveling or other activities. In terms of cost, portable computers are affordable by the individual but they are usually more expensive than personal computers because of their smaller size. The storage size of a portable computer is comparable to a personal computer but it is usually slightly less. Like PCs, notebooks have monitors, keyboards, mice but these are usually all attached to the system to enhance portability and reduce size. The processors of modern portable computers are usually 32-bit or higher with speeds just slightly less than PCs.
Network Computers (Servers) - It is difficult to classify this type of computer under one of the traditional classes. The closest comparison would be somewhere between a minicomputer and microcomputer or sometimes even a mainframe depending on how powerful the computer is. The following is a description for computers between the range of a minicomputer and a microcomputer. The most commonly used name for this type of computer is a server. These computers are used to administrate and control local area networks or wide area networks. Servers have a wide range of processing power. Sometimes for smaller networks, top of the line PCs are used while in larger networks larger computers close around the minicomputer class are used so it is difficult to specify processor speed. However, this is usually better than the average PC. Servers are intended to be used by multiple users within the network but these servers are usually accessed by multiple clients indirectly from other computers rather than being accessed directly. Since servers have to perform much of the administration within a network and store a lot of information, they usually have a large storage capacity. Information is often backed up between a group of servers or on disks because of the importance of this data. Input/output devices are similar to a PC but there are some devices which can be shared among several computers within the network such as a printer. The cost for a server varies depending on the size of the network but it is usually slightly more expensive than the average PC.
Mainframe Computers - This type of high-level computer performs intensive computational tasks. They are intended to be used by many users directly through a terminal or indirectly from another computer in a network. They are usually used by large companies or institutions to perform extremely complex computational tasks or they are sometimes the center of a large network. These computers are very expensive and can contain a very large amount of data. Data is often backed up among a group of computers to ensure that if one fails the other one will have the backed up data. Multiple terminals are used for direct input or output or other computers within the network can access the mainframe indirectly. The processing power of a mainframe is significantly higher than a minicomputer or a microcomputer. In today's modern world, mainframes are not necessarily always large computers. Often a group of minicomputers is considered to be a mainframe.
Supercomputers - This name is used to describe the most powerful mainframe computers. These computers perform the most complex tasks of any computer and they are only used by large corporations or institutions.
(Microsoft Encarta 97 Encyclopedia, 1997)
2.3.3 Definitions for a Network
Local Area Network (LAN) - A computer network where all the computers are directly linked by cables and/or microwave transmission. This is usually located on a user's premises within a limited geographical area. Eg. A network of computers within a small office.
Wide Area Network (WAN) - A network that provides communication services to a geographic area larger than that served by a local area network or a metropolitan area network, and that may use or provide public communication facilities. Eg. The Internet is WAN that encompasses the entire world.
server - a computer that provides services to another computer connected over a network.
client - a component that requests the service of a server.
(IB Computer Science Syllabus, 2000, p.60-75)
2.3.4 Principles of Networking
Left: Bus network
Center: Star Network
Right: Ring Network
Network Topology (Configuration)
Networks can be organized in several different configurations or patterns (network topology). Three distinct configurations for a local area network are the star network, bus network, and ring network. In a star network all computers are connected to a central computer and all data goes through the central computer which routes it to other computers. In a bus network all computers in the network are connected through a main communications line (bus). Each computer monitors activity on the main line and all computers may detect data for a specific computer. Token passing is used to prevent data collisions in the communications line. In token passing, a token is passed from one computer to another. Only computers with a token can transmit data. In a ring network all computers are set up in a ring pattern. Data is sent from one computer to its neighbour on the network and that computer sends it to the next computer in the network. This process is repeated until the data reaches the specified computer. A combination of these configurations can be used to create new topologies. There are a few other basic network topologies besides these three. Another configuration that exists is for only two computers. This configuration is point-point which directly transmits data between two computers.
Network Hardware
Each device that is capable of communicating with other devices within a network is called a node. An example of this is a computer within a network. Computers in a network are linked through some sort of communication link which can be cables, microwaves, fiber optics, etc. Each computer contains a network adapter that accesses the physical media which links computers. Also, the network adapter receives data from the network software, and transmits instructions and requests to other computers. All the nodes in a network are sometimes connected to a hub which passes data from one destination to another.
Sometimes a network may have different segments and in these cases a router is required. A router connects one segment of the network to another segment. In order to do this, the router interprets protocol information and transmits the data through the most efficient route possible.
Network Software
One of the functions of network software is to establish protocols. These protocols are rules that computers follow for communication between each other. Other functions the software performs are allowing computers to interface with each other and permitting information sharing.
Networks are prone to hacking and outside tampering so there must be some form of security to safeguard the network. One method that network software uses to increase security is encrypting data sent over the network. Another common safeguard provided by network software is the management of authorized users and passwords. Access may be restricted in a network by only allowing authorized users with valid passwords to access the network. In addition, the software can control the level of access each user is authorized.
(Microsoft Encarta 97 Encyclopedia, 1997)
2.3.5 Benefits of Sharing in a Network
One of the main benefits of a network is the ability to share programs, data, and resources. Sharing things over a network provides easy exchange of data between computers. A computer with data required by a user using another computer does not have to be accessed directly because the data can travel through the network. Sharing can make information more portable and accessible. By storing information in a central server, the information can be accessed by any other computer within a network. Costs could be cut by sharing resources instead of having the same resource for each computer. For example, several computers could share the same printer instead of using a separate printer for each computer. Another benefit of sharing is a program could be stored in one computer and accessed by other computers. This would save storage space because the program would only have to be on the hard drive of one computer.
2.3.6 Comparison Between the Benefits and Limits of LANs and WANs
Determining the benefits and limits of LANs and WANs often depends on the situation where they are used. The benefits of a LAN are setting up and maintaining it is easier, it is less expensive, it is more secure, and information can be usually exchanged more quickly compared to a WAN. The main limitation of a LAN is its limited scope. On the other hand, the benefits of a WAN are more computers can be connected to the network and a WAN can cover a larger area. The disadvantages of a WAN in comparison to a LAN are decreased security, increased complexity and problems, and usually lower performance.
2.3.7 Applications and Implications of Networking for
Organizations
Organizations often have more than one computer. If multiple computers were not connected then their usefulness is reduced because they are unable to communicate with each other. Networks increase efficiency in an organization by allowing greater communication and the exchange of data between computers. An example of the benefits of a network in an organization is one printer could be used by several computers which would be more efficient and cheaper than using a separate printer for each computer. Another example is communication within an organization is made more convenient and efficient through email because messages intended for multiple users could be easily distributed. All of this increased efficiency leads to increased cost efficiency within an organization or business. However, one of the main disadvantages of using a network are the computers within the network are more prone to security risks from within and outside the network.
2.3.8 Web Browsers and Search Engines
Browsers present formatted texts, images, sounds, video, hyperlinks and other objects from web pages on the Internet. Most web pages are formatted using hypertext markup language (HTML) which uses a set of rules or protocols known as Hypertext Transfer Protocol.
With the enormous size of the Internet a method of searching for information is required. This function is performed by search engines that search for requested information. These search engines often use different search algorithms so results may vary.
2.3.9 Batch Processing, On-line (Interactive) Processing, and
Real-Time Processing
batch processing - a method of processing data in which transactions are collected and prepared for input to the computer for processing as a single unit. Eg. Processing bank transactions.
on-line processing (interactive processing) - data processing in which all operations are performed by equipment directly under the control of a central processor. Eg. Processing airline reservations.
real-time processing - the manipulation of data that is required or generated by some process while the process is in operation; usually the results are used to influence the process, and perhaps related processes while it is occurring. Eg. Air traffic control and monitoring patients in a hospital
(IB Computer Science Syllabus, 2000, p.60-75)
2.3.11 Master and Transaction Files
A transaction file is usually a temporary file containing specific information or transactions for a particular period of time. This file is combined with other files into a master file later on. A master file is a single unit which contains all the updated information from different transaction files. Combining both of these files is referred to as batch processing. An example of this is a transaction file that contains client transactions for a bank is temporarily stored on a computer in a bank during the day. Later on in the night, the transaction file is added to a master file at the bank's central computer station along with other transaction files from other bank branches.