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TEXT A. COMPUTER HARDWARE
There are three basic types of computers: mainframes, minicomputers, and microcomputers (personal computers). Although each of these types of computers functions in much the same way, they differ in terms of size, speed, and cost. All computers process data using some kind of central processing unit, and they all provide methods for storing data. Computers must also provide specialized devices that humans can use to communicate with the processing hardware. A computer system's hardware includes the following components: the central processing unit and it's related processing components, input devices (such as a keyboard or a mouse), output devices (such as a display monitor or a printer), and secondary storage devices (such as a diskette drive, a fixed-disk drive, or a magnetic tape drive). A computer usually uses two types of solid-state, chip-based memory: RAM (random-access memory) and ROM (read-only memory). The computers uses RAM to temporarily storage program and processing information. This information is lost when the computer is turned off. ROM contains permanently stored information such as instructions that are needed for the computer's operation. Computers use a data encoding system that is based on a two-state binary system. Information in this system is represented through the use of ones and zeros. The digit 1 stands for on (the presence of an electronic signal), and the digit 0 stands for off (the absence of an electronic signal). When using magnetic media such as disks and tapes, these two states are indicated through the use of one or two magnetic polarities. When computers store data in a binary representation, each letter, number, and special character is stored based on a coding system. The two most commonly used coding systems are American Standard Code for Information Interchange (ASCII), and the Extended Binary Coded Decimal Interchange Code (EBCDIC), which is usually used only on large mainframe computers. The smallest unit of data that a computer can deal with is known as a bit, but generally computers deal with bits in groups of eight, referred to as a byte. As a result, data management and storage capacities are usually measured in bytes. The term secondary storage refers to devices that are used to store data and program files for longer periods of time. There are many different types of tape drives. Humans interact with the computer's processing hardware with the help of input and output devices. The most common input devices are the keyboard and the mouse. Pointing devices like the mouse were developed when the first graphical uses interfaces came into use. Today, there are a number of new types of input devices based on digitizing technology that allow the user to transfer text and images from hard copy into a form that can be used by the computer. The most common types of output devices, which are used to get information out of the computer in a form usable by humans, are the display monitor and the printer. Both of these output devices come in many different types. The image quality of both monitors and printers is determined by the number of horizontal and vertical picture elements (pixels) available. More pixels result in a higher resolution. Likewise, the image quality of printed output depends on the number of printed dots the primer is capable of producing within a given space (the most common measure of primer capability is dots per inch, often abbreviated as dpi). Ergonomics is the study of how humans interact with machines like computers. Since today's computer users may be interacting with the computer and its devices for many hours at a time, ergonomic considerations should be taken into account whenever a computer system is installed.
TEXT B. THE COMPUTER'S COMPONENTS
As we have seen, a computer is a device used to manage the world's information. But a computer is more than one device; in addition to the main computer itself, it includes a group of devices that are used to get data into and out of the computer.
Devices that are used to get information into the computer are known as input devices; those used to transfer information out of the computer in a form useable by humans are known as output devices. The computer along with its related devices is known as a computer system. The physical components of the computer system are known as hardware; that includes the computer itself and/or its related devices.
Processing Hardware. Almost all of today's computers, large and small, are based on a design that couples some sort of central processing device with a memory area that is used to temporarily hold instructions and data that can be used during processing. And, although today's processors are far more capable that the ones used in the first computers, this basic design has been in use since the early days of computing.
The Central Processing Unit. Today's computers are designed around a single large-scale processing chip known as the central processing unit (CPU). At the microscopic level, many circuits and processing capabilities are incorporated into one chip that may only be one or two inches square. The CPU can be thought of as the "brains" of the computer: if directs most of the computer's information-processing activity.
Each new generation of CPUs has added new processing capabilities, and yet, despite this increased capability, each new generation processes information faster. Over the years, as new, faster processing methods were invented, new ways of miniaturizing the required circuits were also devised. This miniaturization, along with now processing techniques, has resulted in ever smaller, faster computers. Microcomputers that you can now carry in your briefcase have more processing power that computers that used to be as big as a room. And, because many more computers are sold today, their cost has come down significantly.
Today's CPUs are complex devices composed of many different components and circuits that carry out a great variety of functions.
Main Memory. In today's computers, the CPU acts on instructions that are retrieved form a storage system known as main memory. The CPU also uses this main memory to store data temporarily as it carries out-processing tasks. In today's computers, this temporary storage system is based on sets of silicon chips. Each chip is actually made up of millions of circuits that store data in a coded format. Because data stored using this type of primary storage can be accessed at any time, in any order, it is also known as random access memory (RAM).
Secondary Storage System. Secondary storage devices store data not currently being processed. While the computer's main (primary) memory provides temporary storage, the secondary storage systems are used for more permanent data storage. Usually based on magnetic disks of magnetic tape, secondary storage is often used to store data and program files.
The most common type of secondary storage systems in use today is based on magnetic disks. As these disks rotate inside a disk drive, the computer interacts with the drive to retrieve data from the disk or to send new data to it.
Diskette Drives. Diskettes (also known as floppy disks) are a form of storage that can be inserted into a computer that has a compatible disk drive. Some personal computers use a 5 1/4-inch diskette housed inside a flexible plastic jacket; however, the trend is toward smaller 3 1/2-inch diskettes enclosed in a hard plastic case. Both types of diskettes use the same thin, flexible disk inside, but their capacities can vary from 360,000 bytes to more than 2 million bytes.
Fixed Disk Drives. Fixed disks (also known as hard disks) are very similar to diskettes but they are fixed permanently inside the computer. Fixed disks use one or more spinning platters that are very much like diskettes, but they can hold far greater amounts of data.
Magnetic Tape Drives. Magnetic tape drives were one of the first storage devices that used magnetic media, and many of today's large computers still use them. Because the very long tapes provide far more surface area than disks, they can hold far more data (for that reason, they are often used for backing up data; that is, for making a second copy for safekeeping).
Optical Disk Drives. Some newer storage devices use a nonmagnetic technology that is based on optical disks. Optical disks are far more durable and they can be used to store significantly more information.
Today, CD-ROM (computer disk — read-only memory) systems are becoming a popular peripheral for use with microcomputers. These systems use a disk that looks just like the well-known music CDs and can hold more that 500 megabytes (million of bytes) of data. These disks are especially useful when there is a need to store large amount of information — such as a complete encyclopedia — on a single disk.
TEXT C. INPUT AND OUTPUT DEVICES
Devices that are used to get information into the computer are known as input devices. Input devices are used to convert information from a form used by humans into a form that is useable by computers.
Today, there are many different ways to get information into the computer, but the keyboard, a device that has been part of computer systems for many years, is still one of the most common input devices. The computer mouse is another input device that is becoming almost as common as the keyboard. It is referred to as a pointing device.
Unlike the keyboard — which is used to enter data one character at a time — a pointing device is used to move a pointer around on the display screen; when the screen pointer is resting on a name or an image on the screen, a button can be pressed to select the option or activity that is represented. In addition to the mouse, a number of other types of pointing devices for computers are also in use today.
Several other types of devices can be used to convert data into a digital form that can be used by computers. Data that exists in the form of characters or pictures on paper, as bar codes printed on packaging, ore the magnetic patterns stored on credit cards can all be read by special devices and converted into a form that can be used by computers.
Output devices are used to get information out of the computer in a form useable by humans. The display monitor and the printer have long been the computer's primary output devices. Today, they still represent the two most common ways to get information out of a computer, but the type and variety of both monitors and printers are in constant change.
Computer display monitors are the computer's main output devices. Based on the same king technology used in television sets, the early display monitors could only produce characters in one color on a black background. Today, computer display monitors can present information in many colors and in many forms, includes pictures.
These new output capabilities have led to a number of new computer applications that provide a way to create, display, and print pictures on the computer screen. Computer-aided design (CAD) programs are used to create engineering drawings and blueprints, paint and draw programs provide a set of software tools that can be used to create on-screen pictures, and presentation graphics programs can be used to turn numbers into charts and graphs.
Computer printers have also evolved as computer users sought better-printed representations of what they saw on the display screen. Data that is printed out on paper using a printer controlled by a computer is known as output, or hard copy.
Today, there are many different types of computer printers in use but they can generally be categorized as impact or nonimpact.
The most common type of impact desktop printer is the dot-matrix printer.
This type of printer places a dot on paper when one of a group of pins on the print-head strike through an inked ribbon. A series of these dots are used to represent characters or graphic images.
Another impact printer is the letter-quality printer. Letter-quality printers also place ink on paper by striking through an inked ribbon using strikers embosser with letters (like a typewriter).
Nonimpact printers produce an image in paper without using a striking device. Laser printer are a type of nonimpact printer. They have been available for some time, but they are now becoming more popular as the price of this printing technology has come down. Using a technology developed in dry-toner copying machines, laser printers are faster and quieter than impact printers and generally produce a high quality output.
Another nonimpact printer that is growing in popularity is the ink-jet. This type of printer places one dot at a time, but instead of using pins to strike through an inked ribbon this type places droplets of ink on the paper.
A number of other new nonimpact printer technologies are also now in use on under development.