| Information and Computer Technology Fact Sheets |
What is the difference between peripheral hardware and system hardware?
Peripheral hardware are the equipment components that are not essential to the basic operation of the computer but that may be necessary to perform certain applications. Peripheral hardware includes printers, scanners, and modems. System hardware, which was described in Technology Fact Sheet Number 3, is the basic equipment -- or components -- needed to make the computer operate. This includes the computer itself, also called the central processing unit or CPU; the monitor or display terminal; the storage media or disks; and the input device, usually a keyboard or mouse.
What should I look for in a printer?
The printer is probably the single most important peripheral device because it so integral to the operation of the computer. Printers will be covered in more depth in a future Technology Fact Sheet so this will be just a brief introduction. The chief considerations in buying printers are: quality, speed, noise, and adaptability.
Quality or resolution is measured as dots per inch (DPI). The higher the DPI, the better the quality. Printers with 300 DPI are about the norm. Lower quality printers can be used for printing drafts, citations from literature searches, and other non-essential documents. The higher the DPI, the more expensive the printer.
Speed is measures in pages per minute (PPM) or characters per second (CPS). Speed may not
be an issue if a high volume of printing is not expected. Noise is a consideration if the printer is being placed in a work area. Dot matrix printers (see below) are the noisiest; laser printers are very quiet.
If you are asking your printer to do a lot, be sure it can handle labels, envelopes, or oversized papers.
Sharing printers often makes very good sense. Printers can be shared by wiring them to the computers via a switching box or print buffer or by connecting them to a network.
What are the different kinds of printers?
Dot-matrix printers are generally inexpensive workhorses that were popular in the early 1980s when personal computers first became affordable and readily available. They are impact printers that resemble a typewriter but the dot-matrix printers use up to 24 metal pins and an inked ribbon. The pins receive instructions from the software application and can be combined in a variety of ways to print lines, curves, images, and characters. Dot matrix printers are noisy and their quality is lower than that of laser printers but they are reliable, efficient, and versatile. They use paper that is perforated along the side and is fed through the printer on tracks. A device called a "sheet feeder" that feeds one sheet of paper at a time can be attached. These printers are more compact than the laser printers.
Laser printers generate high-resolution output quietly and quickly. They print on single sheets of paper. The price of laser printers is tumbling but the operating costs remain higher than the dot-matrix printer. Lasers require expensive cartridges containing print toner, the laser equivalent of ink. Toner is hard to obtain in many African countries and must be imported at high-cost. Dust and humidity can affect the performance of laser printers.
Other printers include daisy wheels, ink jet, and thermal printers. Ink jets are relatively low cost with high quality and are portable. Thermal printers require special paper that may be expensive and difficult to obtain in Africa. Plotters, which are used by architects and engineers, create elaborate and colorful floorplans and illustrations.
What is a scanner?
Scanners are special input devices that allow the user to transfer photographs, images, or text from a printed source into the computer. The scanner converts the printed image to an electronic form that the computer can use and that the operator can manipulate and store.
Optical character readers (OCRs) are special scanners that recognize the shape of letters. They work by scanning printed text and converting it electronically into data that can be read by the computer. Use of an OCR can minimize the amount of direct input or re-keying that may be necessary when text is not yet in electronic form. Most low-cost scanners do not include OCR; the user is getting only an image of the text.
What is a modem?
Computers can communicate with each other over phone lines; that is, they can share and transfer data over the telephone. To do this, however, both the sending and receiving computers must have a modem (modulator/demodulator) that converts the computer information into audio signals. These signals then travel over conventional phone lines to a modem attached to another computer. This modem converts the audio signals back into information that the computer can recognize.
An internal modem is an enhancement card that snaps into one of the slots inside the CPU. External modems are little boxes that attach to one of the ports on the CPU. Either kind of modem must be connected to computer and to a telephone line. The speed with which the modem transfers information is measured in bits per second (BPS) -- also called baud rate. Baud rates of 300, 1200, and 2400 are common on modems operating in Africa; although modems as fast as 9600 and 19,200 are available. The cost of high-speed modems is decreasing rapidly; this can mean big savings in transmission time. Where the line quality is poor or of variable quality, a high-speed modem will adjust to a slower speed to transmit the data.
To use a modem, a user must also have special communications software that, in effect, converts the computer into a telecommunications terminal.
What are some other peripheral devices?
CD-ROMS are described in detail in Technology Fact Sheet, Number 9.
Uninterruptible power supplies (UPS) are devices that insure a steady and clean supply of electricity to a computer. A sudden loss of or change in power can destroy data and cause damage to a computer. UPSs give the user time to exit from all active applications and save all current data in the event of a power outage. Many computers have some internal protection against power surges. Users can also plug their equipment into surge-protector power strips. Only a UPS, however, offers standby power if there is a power outage. A UPS is a sophisticated battery that augments power or compensates for sudden losses in electric flow. UPSs will be covered in detail in a future Technology Fact Sheet.
Furniture/accessories can consume resources but can also make the computer easier and more comfortable to use. Retractable and adjustable platforms for monitors and keyboards can ease eye-strain and help prevent repetitive stress syndrome. Cables and power lines are needed to connect all the various pieces. Computer magazines and catalogs are a good source of information.