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Large companies and businesses don't usually have just one large computer. Typically, they have a range of specialized computers that are networked. Depending on the size of the company, there could be one or two very powerful mainframe computers, a number of small, medium and large Unix-based midrange computers, and many individual personal computers (PCs).
In fact, most organizations' computers are networked. The network that connects computers in one location is usually referred to as a local area network (LAN); connected individual LANs are a wide area network (WAN). A WAN is made up of servers, workstations, a network operating system, and a communications link. Servers are high-speed machines that hold programs and data shared by network users. Using this network, authorized personnel can access data and make use of computer facilities anywhere in the distributed enterprise.
Until 15 or 20 years ago, mainframes were the most common computers in business. Today's mainframe computers generally run older computer applications (often called 'legacy' systems) that were written several years ago. Depending on the system requirements, these applications are designed to operate on the mainframe, midrange computers (servers) or networked personal computers.
Currently, with appropriate authorization, users can access data files via their computer, regardless which type of operating system their data resides on.
The Internet has revolutionized the computer and communications world like nothing before it. The invention of the telegraph, telephone, radio, and computer set the stage for this unprecedented integration of capabilities. The Internet is a medium for worldwide broadcasting, and for collaboration and interaction between individuals and their computers without regard to geographic location or time restraints.
Today businesses, academic institutions and people at home use the Internet to send e-mail messages around the world, and to conduct research. However, most businesses consider the Internet too slow, unreliable and insecure for widespread internal use. To solve this problem, they have set up their own private internal internets, known as intranets. These intranets provide the convenience of the Internet, along with the performance and security of an in-house system. Intranets can be connected to the public Internet via secure gateways, which have 'firewalls' to prevent unwanted external access to internal systems.
To function properly, a computer system needs the following hardware components:
Data can be entered into a computer through a range of ways, including:
The Central Processing Unit (CPU) is the heart of a computer system. In most modern computers, the CPU consists of just one or two silicon chips that are small enough to hold in one hand, but contain many millions of logic circuits. A CPU can execute millions of instructions per second.
Associated with the CPU is the random-access memory (RAM). The RAM has to be big enough to hold all programs and data that are being worked on at any given time. RAM size ranges from a few million bytes to a few hundred million bytes.
Disk drives are used by computers to store data. A current PC might have a 2.0-gigabyte (GB) disk drive (20 billion bytes), while large computers might have a number of disk drives holding tens or hundreds of gigabytes.
Data can be copied onto magnetic tape or CD-ROMs for backup, transfer between computers, or long-term storage. A CD-ROM can hold 700 megabytes (MB), while tape units can range from about 500 MB to 24 GB. Data can also be copied onto diskettes (floppy disks), but their small size (1.44 MB) limits their usefulness with large data sets.
An output device is any peripheral device that presents output from the computer. Output devices include:
Computers can also be used to drive industrial processes, control chemical plants, and lock/unlock security doors. Modern car-engine management systems, office elevators, VCRs, and numerous other domestic and industrial systems are now controlled by miniature computer systems.
Much of the computer's power comes from its ability to store, sort and classify data. Over the past few years, disk systems have become very inexpensive and reliable and it is now possible to obtain disk systems that will store billions of bytes of data for just a few hundred dollars. This thousand fold drop in price has greatly improved the usefulness of computers. It is now possible to hold all of a company's information, going back for years, on a computer.
There are two basic types of computer software: systems software, which controls the operation of the computer, and applications software, which performs useful tasks for the user.
Systems software itself is divided into two classes: operating systems, and tools and utilities.
An operating system generally has two levels:
Typical operating systems include DOS, UNIX, Mac OS and Windows. Mac OS and Windows have a user-friendly graphical user interface (GUI) which enables computer control by means of windows, menus, icons and a mouse. DOS and UNIX require the user to type precise commands, which can be hard to remember. Windows, Mac OS and UNIX can run many programs at one time (multiprogramming), which makes for more efficient use of computer hardware and more convenience for the user.
Tools and utilities software are usually necessary to make productive use of a computer. Some of the software are provided with the operating system, while others can be downloaded or purchased separately. Typical system utilities include Internet browsers, antivirus software, program compilers, editors and file-backup systems.
Applications software can also be divided into two classes: personal productivity tools and other computer applications.
are commercial products designed to handle standard computing tasks such as word processing, numerical analysis, data manipulation and storage, and data presentation. Typical products include:
Personal productivity tools are used at home, at school and in the office. These tools are fairly inexpensive and available on many computers. However, businesses and organizations usually buy computers to automate major business functions, not handled by personal productivity software.
Some software applications can cost many thousands of dollars to buy or develop, while a major banking or airline reservation system could cost millions. Application software can be purchased 'off the shelf' or developed for a specific purpose. An accounting package is an example of a purchased application, while a system to handle parking fines might be designed and written from scratch.
An example of a complex computer application is an airplane's autopilot navigation system. This system's software receives information (e.g., compass heading and Global Positioning System data) and outputs data that controls rudder and flap hydraulics which adjust the course of the plane.
If it is decided to develop software to automate a task, the work is done by systems analysts and programmers.
Systems analysis is the process of breaking down a data-processing problem into functional components to determine the best method of handling the problem. Systems analysts design and modify systems by turning user requirements into a set of functional specifications, the blueprint of the system.
In consultation with the user, the systems analyst must:
Programming is the process of producing a set of instructions to make a computer perform a specified activity. Programmers take system analysis results and develop computer programs to solve the problem.
In consultation with the user, a programmer must:
The user is the final judge of whether a computer system is meeting the needs it was designed to fulfill. The better the link between the automated system components and the user, the more likely it is that the system will be effective. Modern system designers consult widely with users in order to design systems that meet their needs, and designers put considerable effort and ingenuity into designing the interface between systems and users.