Computer Hardware 54.1 Defining Computer Hardware

The computer hardware is the equipment and devices that make up a computer system as opposed to the programs that are used on it. A digital computer is not a single machine: rather, it is a system composed of distinct elements.

• input devices

• central processing unit

• primary storage devices

• secondary storage devices

• output devices

• communication devices

In order for information to flow through a computer system and be in a form suitable for processing, all symbols, pictures, or words must be reduced to a string

of binary digits. A binary digit is called a bit. It represents the smallest unit of data in a computer system. It can only have one of two states (e.g. true or false, on or off), represent ed by 0 or 1. A byte is a string of eight (8) bits, used to store one number or character in a computer system.

Computers continue to become smaller, faster, more reliable, less costly to purchase and maintain, and more interconnected within computer networks. input devices are directed toward direct data input that ids more natural and easy to use, while output devices are geared toward direct output methods that communicate naturally, quickly, and clearly.

54.2 Input Devices

Input devices enable a computer user to enter data, commands, and programs into the CPU. Included in this category are the following.

• Keyboard - This is commonly known as the QWERTY keyboard, named after the six leftmost characters in the top row of alphabetic characters on most keyboards-the standard layout of most typewriters and computer keyboards. An alternative layout, the Dvorak keyboard, is considered more efficient, but the QWERTY keyboard has the advantage of familiarity.

This is the most common input device. Information typed at the typewriter-like keyboard is translated by the computer into recognizable patterns.

• Mouse - This was invented by Douglas Englebert and was popularized by its inclusion as standard equipment with the Apple Macintosh. It helps a user navigate through a graphical computer interface. It is generally mapped so that an on-screen cursor may be controlled by moving the mouse across a flat surface. There are many variations on mouse design, but they all work in a similar manner. Some mouse units feature a scroller, which provides a better way of scrolling through documents vertically and/or horizontally. The latter optomechanical mouse eliminates the need for many of the wear-related repairs and maintenance necessary with purely mechanical mice.

• Joystick - This performs the same function as the mouse. It is favored for computer games. A joystick usually has a square or rectangular plastic base to which is attached a vertical stem. Control buttons are located on the base and sometimes on top of the stem. The stem can be moved in all directions to control the movement of an object on the screen. The buttons activate various software features, generally producing on-screen events. A joystick is usually a relative pointing device, moving an object on the screen when the stem is moved from the centre and stopping the

movement when the stem is released. In industrial control applications, the joystick can also be an absolute pointing device, with each position of the stem mapped to a specific on-screen location.

• Trackball - This can be roughly described as a mouse on its back. It consists of a ball resting on two rollers at right angles to each other, which translate the ball's motion into vertical and horizontal movement on the screen. It typically has one or more buttons to initiate other actions. The only functional difference between a mechanical mouse and a trackball is in how the ball is moved. With a trackball, the housing is stationary, and the ball is rolled with the hand. A trackball is useful for fine work because the user can exert fingertip control. Another major advantage of a trackball is that it takes up little desktop surface. This replaces the mouse on some laptop computers.

• Graphics tablet - This pointing device is also called a digitizing tablet. It is a flat plastic rectangle with subsurface electronics, used in conjunction with a pointing device in many engineering and design applications as well as in illustration work. When a pointing device, like a puck (or even the finger), is moved on the surface of the tablet, the location of the device is translated to a specific on-screen cursor position.

• Puck - This is often used in engineering applications. It is a mouse-like device with buttons for selecting items or choosing commands and a clear plastic section extending from one end with cross hairs printed on it.

The intersection of the cross hairs on the puck points to a location on the graphics tablet, which in turn is mapped to a specific location on the screen. Since the puck's cross hairs are on a transparent surface, a drawing can easily be traced by placing it between the graphics tablet and the puck and moving the cross hairs over the lines of the drawing.

• Scanner - This input device uses light-sensing equipment to read information in paper or another medium, and translate the pattern of light and dark (or color) into a digital signal that can be manipulated by either optical character recognition software or graphics software. A frequently encountered type of scanner is flatbed, meaning that the scanning device moves across or reads across a stationary document. Another type of flatbed scanner uses a scanning element placed in a stationary housing above the document. Other scanners work by pulling in sheets of paper, which are scanned as they pass over a stationary scanning mechanism, as in the common office fax machine. Some specialized scanners, like barcode readers, work with a standard video camera, translating the video signal into a digital signal for computer processing. Another popular type

of scanner is the hand-held scanner, a scanner held in the user's hand is moved over the document to be scanned.

• Light pen - This is a pointing device in which the user holds a wand, which is attached to the computer, up to the screen and selects items or chooses commands on the screen (the equivalent of a mouse click) either by pressing a clip on the side of the light pen or by pressing the light pen against the surface of the screen. The light pen doesn't require a special screen or screen coating, as does a touch screen, but its disadvantage is that holding the pen up for an extended length of time is tiring to the user.

• Touch screen - This is a computer screen designed or modified to recognize the location of a touch on its surface. By touching the screen, the user can make a selection or move a cursor.. The touch screen's popularity with personal-computer users has been limited because users must hold their hands in midair to point at the screen, which is prohibitively tiring over extended periods. Also, touch screens do not offer high resolution-the user is not able to touch only a specific point on the screen. Touch screens are, however, immensely popular in applications such as information kiosks because they offer pointing control without requiring any movable hardware and because touching the screen is intuitive.

• Card reader - This is a device that can acquire and process information stored in electronic cards like ATM cards, ID cards, special privilege cards, credit and debit cards, and so on. It commonly found in commercial establishments where transaction cards are swiped to obtain necessary information about the customer or client.

• Voice recognition system - It may be any device and software which together, take spoken words and translate them into digital signals for the computer. A typical device used in speech recognition is a microphone.

Speech recognition is the ability of a computer to understand the spoken word for the purpose of receiving commands and data input from the speaker. This method is also fairly reliable provided the speaker's speech patterns are consistent. Speech recognition also allows full speech-to-text conversion.

• Storage devices - can also be used to input data into the processing unit.

An example is the transfer of data from an external storage device to the computer, such as an external disk drive, digital camera with stored images, or any other external storage device.

54.3 Central Processing Unit

The central processing unit (CPU) is the part of the computer system where manipulation of data, (symbols, numbers, and letters) occurs. It also controls other parts of the system.

The CPU may be a single chip or a series of chips that perform arithmetic and logical calculations and that time and control the operations of the other elements of the system. Contemporary CPUs use semiconductor chips called microprocessors, common in personal computers, which integrate all the memory, logic, and control circuits for an entire CPU onto a single chip. The development of the microprocessor was made possible through miniaturization and integration techniques.

The speed and performance of a computer's microprocessor help determine a computer's processing power. These are based on the following.

• Word length - This refers to the number of bits that the computer can process at one time (e.g. a 64-bit chip can process 64 bits, or 8 bytes in a single cycle). The larger the word length, the greater the computer's speed.

• Cycle speed - This is measured in megahertz (MHz) or gigahertz (GHz).

This indicates the number of cycles per second (e.g. a 500 MHz Intel Pentium III processor will have 500 million cycles per second).

• Data bus width - This acts as a superhighway between the CPU, primary storage, and other devices, which determines how much data can be moved at one time. the 8088 chip having 16-bit word length but only an 8-bit data bus width can process data in 16-8-bit chunks but could only be moved 8 bits at a time).

Most CPU chips and microprocessors are composed of four functional sections:

• Arithmetic/logic unit - This gives the chip its calculating ability and permits arithmetical and logical operations.

• Registers - These are temporary storage areas that hold data, keep track of instructions, and hold the location and results of these operations.

• Control section - The control section has three principal duties.

o It times and regulates the operations of the entire computer system

o Its instruction decoder reads the patterns of data in a designated register and translates the pattern into an activity, such as adding or comparing

o Its interrupt unit indicates the order in which individual operations use the CPU, and regulates the amount of CPU time that each operation may consume.

• Internal bus. - This segment of a CPU chip or microprocessor is a network of communication lines that connects the internal elements of the processor and also leads to external connectors that link the processor to the other elements of the computer system. There are three types of CPU buses

o Control bus - This consists of a line that senses input signals and another line that generates control signals from within the CPU.

o Address bus - This is a one-way line from the processor that handles the location of data in memory addresses.

o Data bus - This is a two-way transfer line that both reads data from memory and writes new data into memory.

There are certain ways that can speed up processing.

• Reduced instruction set computing (RISC) - This technology is used to enhance the speed of microprocessors by embedding only the most frequently used instructions on a chip.

• Parallel processing - This is a type of processing in which more than one instruction can be processed at a time by breaking down a problem into smaller parts and processing them simultaneously with multiple processors.

• Massively parallel processing - This is similar to parallel processing, only that hundreds or thousands of processing chips are used to attack large computing problems simultaneously. The manner in which data are input into the computer affects how the data can be processed. Information systems collect and process information in one or two ways.

• Batch processing - This is a method of collecting and processing data in which transactions are accumulated and stored until a specified time when it is convenient or necessary to process them as a group.

• On-line processing - This In this method, transactions are entered directly into the computer system and processed immediately.

Aside from the computer's CPU, another computer hardware that can be considered under this category is the motherboard (or the main board). This is the main circuit board containing the primary components of a computer system. This board contains the microprocessor, main memory, support circuitry, and bus

controller and connector. Other boards, including expansion memory and input/output boards, may attach to the motherboard via the bus connector.

54.4 Primary Storage

Primary storage refers to temporary storage of data and program instructions during processing. It is also known as internal storage since it stores data in the computer memory. There are two types.

• RAM (Random Access Memory) - These are chips that are mounted directly on the computer's main circuit board, or in chips mounted on peripheral cards that plug into the computer's main circuit board. They are called so because the computer can directly access any randomly chosen location in the same amount of time. These RAM chips consist of millions of switches that are sensitive to changes in electric current. So-called static RAM chips hold their data as long as current flows through the circuit, whereas dynamic RAM (DRAM) chips need high or low voltages applied at regular intervals-every two milliseconds or so-if they are not to lose their information. RAM is used for short-term storage of data or program instructions. It is volatile - meaning its contents will be lost when the computer's electric supply is turned off.

• ROM (Read-Only Memory) - These chips form commands, data, or programs that the computer needs to function correctly. RAM chips are like pieces of paper that can be written on, erased, and used again; ROM chips are like a book, with its words already set on each page. ROM is non-volatile. ROM can only be read from it; it cannot be written to. ROM chips come from manufacturers with programs already burned in or stored. ROM is used in general-purpose computers to store important or frequently-used programs. Like RAM, ROM chips are linked by circuitry to the CPU.

Primary storage has three main functions.

• They store all or part of the software program that is being executed.

• They store the operating system programs that manage the operation of he computer.

• They hold the data that the program is using.

Computer storage is measured in bytes. A byte is equivalent to a string of eight bits. If byte is prefixed with kilo (i.e. kilobyte), it becomes 1,000 bytes; such that 100 kilobytes (KB) is 100,000 bytes. Megabyte (MB) is 1,000,000 bytes; gigabyte (GB) is 1,000,000,000 bytes; and terabyte (TB) is 1,000,000,000,000 bytes.

54.5 Secondary Storage

Secondary storage stores data and instructions when they are not used in processing. Relatively, they are long-term, non-volatile storage of data outside the CPU or primary storage. Secondary storage is also known as external storage because it does not use the computer memory to store data. External storage devices, which may actually be located within the computer housing, are external to the main circuit board. These devices store data as charges on a magnetically sensitive medium such as a magnetic tape or, more commonly, on a disk coated with a fine layer of metallic particles.

The most popular secondary storage devices include the following.

• Magnetic disks - This broad category includes the following.

o Floppy disk - The floppy disk in normal use stores about 800 KB or about 1.4 MB.

o ZIP disk - A ZIP disk is much like a floppy disk but has a greater capacity.

o Hard disk - Hard, or "fixed", disks cannot be removed from their disk-drive cabinets, which contain the electronics to read and write data on to the magnetic disk surfaces. Hard disks currently used with personal computers can store from several hundred megabytes to several gigabytes.

o RAID (Redundant Array of Inexpensive Disks) - This is a disk storage technology to boost disk performance by packing more than 100 smaller disk drives with a control chip and a specialized software in a single large unit to deliver data over multiple paths simultaneously.

• Optical disks - These disks use the same laser techniques that are used to create audio compact discs (CDs). Under this genre are:

o CD-ROM - This is an acronym for compact disc read-only memory, a form of storage characterized by high capacity (roughly 600 MB) and the use of laser optics rather than magnetic means for reading data.

o WORM - This is an acronym for write once, read many. This is very much like the CD-ROM. This type of optical disc can be read and reread but cannot be altered after it has been recorded.

WORMs are high-capacity storage devices. Because they cannot be erased and re-recorded, they are suited to storing archives and other large bodies of unchanging information.

o R and RW - In simple definition, these are blank CD-ROM that are ready for data storage. A CD-R is similar to a WORM which cannot be erased or re-recorded. A CD-RW is capable of being erased and re-recorded.

o DVD - This is short for digital versatile disc. The group of DVD disc formats includes various forms of data recording for computer purposes, including discs that contain pre-recorded data (DVD-ROM) and discs that can be rewritten many times (DVD-RAM). These are several times the capacity of CD-ROMs.

The simple single-layer version of the DVD holds between 3.7 and 4.38 GB (with double-layer versions holding 15.9 GB), compared to the 650 MB of CD-ROMs. These higher capacity discs are used particularly for computer games and in multimedia applications.

o DVD-R and DVD-RW - These are blank optical disks in DVD format ready for data storage, just like CD-R and CR-RW.

54.6 Output Devices

Output devices enable the user to see the results of the computer's calculations or data manipulations. They present data in a form the user of the computer can understand.

The most common output device can deliver either the soft copy or the hard copy of the data. Devices that render soft copy are the following:

• Video display unit (VDU) - This is commonly known as the monitor, which displays characters and graphics on a television-like screen. It usually has a cathode ray tube like an ordinary television set, but small, portable computers use liquid crystal displays (LCDs) or electroluminescent screens.

• Audio output devices - These are responsible for the sound that the user hears from the computer. These include the sound card and the speakers.

The sound card is a computer circuit board that allows the computer to receive sound in digital form and reproduce it through speakers.

• External storage devices - These include floppy disks, compact disks,, external hard disks, etc.

• Interactive multimedia - This is the combination of audio, video, and text on high-capacity compact discs. CD-I includes such features as image

display and resolution, animation, special effects, and audio. Interactive multimedia includes the following materials.

o e-books and e-newspapers

o electronic classroom presentation technologies o full motion videoconferencing

o electronic classroom presentation technologies o full motion videoconferencing