Comprehensive Guide to Computer Output Devices

Definition and Classification of Output Devices

Output devices are essential components used to retrieve processed information from a computer system. The term "output" refers to the act of showing, printing, or storing the results of data that has been processed. Output is categorized into two distinct types: hard copy and soft copy. A hard copy is a permanent, tangible form of output, such as data printed on paper, which can be physically handled and reviewed independently of the computer. In contrast, a soft copy is a temporary, intangible form of output. This includes information displayed on a screen or audio emitted from speakers, which cannot be touched.

Display Devices and Screen Technology

Display devices are output devices that present information in a pictorial form. While computers most commonly display output on a monitor or screen, the physical configuration varies; some monitors are separate units that must be plugged into a system unit, while others are integrated directly into the device, as seen in laptops and smartphones. Additionally, televisions can function as computer monitors. Interactive whiteboards, also known as smartboards, are another type of display device used frequently for presentations and teaching. These are large, touch-sensitive plastic boards that respond to input either through a direct computer connection or via auxiliary devices such as projectors, tablets, or magnetic pens.

At a technical level, a monitor contains a matrix or array composed of luminescent dots in red, green, and blue. By blending these primary colors, the device can display millions of colors. A computer image is formed by mapping the location and color information of every bit of data. The final image visible on the monitor is comprised of thousands of individual units called pixels, which stands for "picture element."

Features and Quality of Display Screens

The quality and functionality of a computer screen are determined by several key features. The size of the monitor refers to the physical dimensions of the screen showing the output and is traditionally measured diagonally. Resolution is a critical factor that defines how clear and detailed the output appearing on the screen will be. Because pictures are made of tiny dots or pixels, the resolution is determined by the density of these dots; a higher number of pixels per inch results in a clearer and more detailed graphic. Finally, the cursor is a specific symbol on the screen that indicates the user's current working position.

General Categorization of Printers

Printers are devices used to produce a hard copy by outputting text and images from a computer onto paper. The selection of a printer typically depends on several factors: the required speed, the quality of the output, the quantity of documents needed, and the overall cost. Printers are broadly divided into two categories based on their mechanical method of operation: impact and non-impact printers.

Impact Printers: Line and Character Models

Impact printers function by transferring data onto paper through the use of carbon or an inked ribbon. These machines are known for being noisy and generally do not produce high-quality graphics. However, they are highly useful for specific industrial tasks, such as printing payroll, financial reports, or other documents that require continuous sheets of paper that are perforated for easy tearing. There are two primary types of impact printers:

1. Line Printers: These devices print an entire line of text at one time. While they are characterized by fast operation speeds, they lack the ability to print graphics, and the resulting text quality is not very high.

2. Character Printers: These devices print only one character at a time. A common example is the dot-matrix printer, which utilizes a series of pins to strike an inked ribbon and create a pattern of dots on the paper. The primary advantage of dot-matrix printers is their relatively low cost, though this comes at the expense of poor print quality.

Another specific type of character printer is the daisy wheel printer. This device uses a wheel containing various characters that rotates until the correct character faces the paper. A hammer then strikes the character, forcing it into an ink-ribbon to leave an impression on the paper. Although it produces high-quality text, it is incapable of printing graphics and makes switching between different fonts impractical.

Non-Impact Printers: Ink-jet and Laser Technology

Non-impact printers use methods that do not involve physically striking the paper or an ink ribbon, instead utilizing ink spray or toner powder which may be fixed to the paper using heat. As a category, they are generally faster and significantly quieter than impact printers.

Ink-jet printers operate by squirting very small drops of ink onto the paper to form text and images. This is achieved via a print head containing several nozzles that moves back and forth while the paper passes through. These are commonly used for school work, photographs, and greeting cards. While they offer high-quality output at high speeds for a low initial purchase price, they have disadvantages: the ink cartridges require frequent and expensive replacement, and the need to clean the print head can lead to ink wastage.

Laser printers utilize a laser beam in conjunction with toner (dry ink powder) and a photoconductive rotating drum. In this process, the paper is electrostatically charged to attract the toner, and the resulting pattern is baked onto the paper. Laser printers are favored for producing high-resolution, high-quality documents at very fast speeds while operating quietly. Their main drawback is that they are expensive to purchase.

Thermal Printers and Graphic Plotters

Thermal printers use heat applied to chemically treated paper to form characters. These are specialized devices commonly found in banking machines (ABM) for receipts, and are used for debit or credit card slips and ultrasound machines. They offer the advantages of being quiet and requiring low maintenance, but the specialized paper is expensive and the print eventually fades when exposed to light or heat.

Graphic plotters are output devices that use colored pens or toner to draw images. They are the preferred tool for architects, engineers, and car designers when printing 3D drawings, diagrams, and charts. There are three types of plotters: flatbed plotters (where the paper is held stationary while the ink moves), drum plotters (where paper rolls over a cylinder), and pinch roller plotters (a hybrid of flatbed and drum designs). Plotters can produce large, high-quality drawings very quickly, but they are physically large and expensive.

Specialized Output: Microfilm and 3D Printing

Microfilm is used as a high-speed alternative to traditional printing, often referred to as computer output microfilm (COM). This method condenses vast stacks of paper onto a small roll of film or microfiche without requiring special programming. While this makes the stored text and images human-readable in a compact format, the drawback is the requirement for a special device to print the microfilm and a specialized viewer to read it.

3D printers operate similarly to ink-jet printers but create physical 3D models layer by layer, starting from the bottom and working upward. This process can take many hours as each layer is printed onto the previous one. Instead of traditional ink, 3D printers use melted plastic that adheres the layers together.

Audio Output Devices

Speakers are devices that convert analog audio signals into air vibrations to produce audible sound. This sound can originate from digital files or music CDs. Common examples of speaker-based output devices include headphones, earphones, and earbuds.

Questions & Discussion

1. Explain the difference between Hard copy and soft copy. A hard copy is a permanent, tangible output on a physical medium like paper, whereas a soft copy is a temporary, intangible output such as a visual display on a monitor or audio from a speaker.

2. Give two examples EACH of devices which produce hard copy and soft copy. Examples of hard copy devices include printers and plotters. Examples of soft copy devices include monitors (display screens) and speakers.

3. What are pixels? What important part do pixels play in a quality of the screen? Pixels, or "picture elements," are the tiny dots that make up the images on a screen. They are the fundamental units of resolution; the more pixels there are per inch, the higher the resolution, leading to a clearer and more detailed display.

4. Give an application in which a plotter is used. Explain why a plotter is used instead of a screen. Plotters are used by architects for printing large-scale blueprints and 3D diagrams. A plotter is used instead of a screen when a large-scale, high-quality physical hard copy is required for technical review or construction site use where a digital screen is impractical.

5. A computer store has software that generates invoices. The invoices are to be printed in triplicate using carbon paper. Recommend a printer that is best suited for this application and state why this printer is recommended. A dot-matrix printer (an impact printer) is recommended. This is because impact printers use physical pressure to strike an ink ribbon, which is necessary to transfer the impression through the layers of carbon paper to create triplicate copies.

6. State one (1) use of microfilm. One use of microfilm is to condense large volumes of paper documents into a very small, manageable film format for long-term storage and space-saving.