Program Modul 2

Equipment

A typical computer system can be described by breaking the system into three distinct sections: inputs, processing and outputs.

Inputs are information conveyed to the computer through devices for either manual entry (e.g. game controllers, keyboard, mouse) or digital entry (e.g. imaging equipment such as scanners and digital cameras). Many devices are in general use, however others are developed for more specialised applications (e.g. graphics tablet or magnetic card-reader).

Processing includes executing software program instructions and mathematical processing, which is undertaken by a central processing unit (CPU) that is linked to ancillary processors, memory modules, input and output devices.

Outputs are the means by which processed information is communicated to users (e.g. monitor or printer). Some components fulfil both an input and output role (e.g. network interface cards and either fixed or removable storage devices).

Computers, monitors, printers, scanners and other equipment are described separately in the following sections. Whilst these sections are not intended to form a primer for the manufacture and construction of computer equipment, a number of industry terms and acronyms have been included to facilitate identification of key components, and to provide examples of their use.

1. Computers

Computers are made in a variety of forms to cater for different applications, with the most common forms being desktop computers, laptop or notebook computers, and servers.

Desktop computers are generally comprised of several components connected together to provide inputs, processing and output (e.g. case, keyboard, monitor and mouse).

Laptop computers have integrated input, processing and output devices to allow for ease of transport, and as such are much smaller than desktop computers (i.e. smaller than a briefcase).

Servers are specialised computers that are used to coordinate inter-operation by a number of computers and output devices over a network.

Common components of all three forms include those outlined below.

• A case that encloses the key components of a computer (including the CPU, memory power supply and storage devices), and provides protection from dust or damage. Cases are generally comprised of a metal frame and cover with a moulded plastic faceplate. Some laptop cases are high-impact plastic, whereas others are made of high-grade, lightweight metals like titanium.
• Integrated Circuits (ICs): ICs are the chips that perform the logical and computational functions within a computer. The ICs that are present within a computer include the Basic Input/Output System (BIOS), which is used to control fundamental operations; Random Access Memory (RAM), which is used to temporarily store information during processing; and Read-Only Memory (ROM), which is used to permanently store essential instructions. An IC is made of a silicon wafer and may be housed inside a flat plastic case with metal interface pins, or directly wired to a printed circuit.
• The Central Processing Unit (CPU) is also an IC. The term CPU is often used to describe the case and internal components, however it more correctly refers to the main processor that executes program instructions and performs mathematical calculations.
• Printed Circuit Board (PCB): PCBs are the principal material that contains the computer's basic circuitry and components. The largest PCB is the motherboard, which connects the components of the computer (e.g. CPU, input and output devices, RAM and storage devices) to one another. Expansion slots on the motherboard allow for the insertion of daughter boards that provide further input and output connections (e.g. sound, modem, networking, video). Circuitry is imprinted or affixed to the surface of the board; this involves the use of metals (primarily copper, with gold-plated connectors) to provide the circuit, embedded in a fibreglass board using either glue or solder. Fire retardants are usually incorporated into the manufacture of PCBs.
• Storage: Information can be stored on fixed devices (e.g. magnetic "hard" drive) or removable devices that use any one of a range of consumable media (e.g. 3.5" magnetic disks, CD-ROM, digital tape, flash memory cards and Zip disks).
• Power Supply: The power supply takes mains power and transforms it to the voltages required by the CPU, motherboard and input/output devices. Metal and some plastic components are used in their construction.
• A battery, either as a main source of power supply (e.g. laptops) or as a backup to enable basic functions (e.g. saving times and dates) when the main power is switched off. In the past, nickel cadmium (NiCd) or nickel metal hydride (NiMH) batteries were used; however computers manufactured today generally utilise lithium ion (Li) batteries.
• Two or more fans to cool the CPU, power supply and other heat-generating components. These are generally manufactured from plastic with metal connections.
• Cables to convey power to individual components (e.g. from the power supply to the motherboard) and data from one component to another (e.g. bus cables connecting the motherboard to storage devices). All of these cables are made of metal wires (principally copper) surrounded by plastic.

2. Monitors

Cathode ray tube displays (CRTs) are the predominant display technology currently used in computer monitors. A CRT is generally comprised of a glass panel screen, a plastic casing (often with a swivel base), various connecting wires, magnetic and radiation shielding, and the cathode ray tube itself.

The cathode ray tube holds electron guns and deflection yoke coils, which create an electric field that directs a flow of electrons from the guns through small holes in a shadow mask to illuminate phosphors on the back of the glass panel screen. This tube's glass funnel contains lead for radiation shielding, and is joined to the glass panel screen and shadow mask using a 70-80% lead-content solder. The location of these components is shown

Flat panel displays are an alternate display technology to CRTs that is predominantly used in applications where portability (i.e. weight, size) and energy consumption are important (e.g. laptops). Liquid crystal displays (LCDs) are a type of flat panel display where the monitor produces an electric field to trigger a grid filled with crystals, with the resulting arrangement of crystals forming the desired image on the screen. Figure 2.3 indicates the principal parts of an LCD screen.

An LCD screen is comprised of electrodes on two glass substrates with liquid crystals sealed into the narrow gap between them. There are approximately 300 different liquid crystal compounds used, comprised of non-hazardous organic chemicals. The common LCD technology used in computer monitors uses separate and independent Thin Film Transistors as a switch for each pixel. Turning these switches on or off will align the liquid crystal molecules so that light from the screen's backlight is allowed to shine through to a coloured filter and then to the front of the display. Up to four fluorescent lamps and a thin light diffuser are used to provide light so the screens may be seen in the dark. This assembly is sandwiched within a metal frame for protection and ease of mounting.

3. Printers and Cartridges

Printers download digital information from a computer onto paper, generally through one of three processes, namely dot matrix, inkjet and laser printing.

The dot matrix or impact system is akin to a typewriter, with a printhead impressing a combination of tiny pins onto an inked ribbon to form characters and images. Machines of this type were historically the least expensive option to purchase, however the comparatively low quality of the printed material and the decline in cost of inkjet printers has led to a considerable decline in use over recent years.

Inkjet printers use cartridges that are comprised of a supply of ink and a printhead of tiny jets embedded with electronic heating elements that force the ink onto the page. The quality of images that these printers are capable of delivering, combined with the relatively low cost compared to laser printers, have led to this printer becoming the dominant type for low-volume users.

Laser printers use a laser to describe an image onto a drum, which induces a negative electrical charge on the drum surface that causes the positively-charged toner particles to adhere to it. The toner is transferred to paper as it passes over the drum, and a heat roller then fuses the toner to the paper. The rapid delivery of printed material that this process allows has led to laser printers becoming the dominant printer for high-volume users.

Printers and their cartridges are predominantly made from moulded plastic with metal parts. Laser toner cartridges also contain a glass drum that has been chemically coated to impart particular charge and thermal related properties.

4. Scanners

A scanner is a device that takes in an optical image and digitises it into an electronic image. This can be used to create a computerised version of a photo or illustration. It may also be linked to optical character recognition software allowing printed documents to be converted to electronic text without keyboard entry. There are a number of different forms of scanner, including handheld and 'flatbed' readers. They are generally comprised of a moulded plastic housing with a glass copy plate, a bright scanning light and PCBs with control ICs.

5. Cabling

In addition to the cables present within a computer case, there are cables for the transmission of power (e.g. from the mains electrical socket to a computer power supply, monitor, printer, etc.) and data (e.g. from the printer port of the computer case to the printer, or from the video output to the monitor). These cables tend to be in short lengths and are generally comprised of copper wires with a sheath of plastic insulation.

Copper cabling is also used in the interconnection of two or more computers to form a network. Alloys used in copper cable vary greatly, with the percentage of copper used proportional to the distance between connections and the quantity of current that the cable is expected to carry.

Fibre optic cabling, where the glass conducts data as pulses of light, is also used in the creation of large networks. The majority of applications for optical fibres lie in the telecommunications sector and, whilst there are specialised adapter cards available to network PCs using optical fibre, it is rare for cabling of this sort to be directly connected to desktop computers, laptops or servers.

6. Other Devices

Handheld computers are compact integrated devices designed for portability and usually for inter-operability with desktop or laptop computers. They are generally sized to fit within the palm of one hand. A variety of forms exist, however the common components are a battery, ICs, LCD and a PCB within a high-impact plastic case.