Operating Systems Communicate With Most Hardware Components Using Blank

Introduction

Hardware is the almost visible part of whatsoever information arrangement: the equipment such equally computers, scanners and printers that is used to capture data, transform it and present it to the user as output. Although we volition focus mainly on the personal computer (PC) and the peripheral devices that are unremarkably used with it, the same principles apply to the complete range of computers:

• Supercomputers, a term used to denote the fastest calculating engines available at any given time, which are used for running exceptionally demanding scientific applications.
• Mainframe computers, which provide loftier-chapters processing and data storage facilities to hundreds or even thousands of users operating from (dumb) terminals.
• Servers, which have large data storage capacities enabling users to share files and application software, although processing will typically occur on the user's ain machine.
• Workstations, which provide high-level functioning for private users in computationally intensive fields such equally engineering.
• Personal computers (including laptop/notebook computers) have a connected monitor, keyboard and CPU, and have developed into a convenient and flexible business tool capable of operating independently or as part of an organizational network.
• Mobile devices such every bit personal digital assistants or the latest generation of cellular telephones, offering maximum portability plus wireless connectedness to the internet, although they do not offer the full functionality of a PC.

And nosotros are already moving into the age of wearable computers for medical or security applications, embedded computers in appliances ranging from motor cars to washing machines, and the smart bill of fare which will provide identification, banking facilities, medical records and more than!

Input devices

Data may enter an information organization in a variety of dissimilar ways, and the input device that is most advisable will usually depend on the type of data beingness entered into the system, how oft this is done, and who is responsible for the activity. For instance, information technology would be more than efficient to scan a page of typed text into an data organization rather than retyping it, but if this happens very seldom, and if typing staff are readily available, and so the cost of the scanner might non exist justified. However, all of the input devices described in this chapter have at least one thing in common: the power to translate non-digital data types such every bit text, sound or graphics into digital (i.e. binary) format for processing by a computer.

The keyboard

A lot of input still happens past means of a keyboard. Usually, the information that is entered by ways of a keyboard is displayed on the monitor. The layout of most keyboards is similar to that of the original typewriter on which it was modeled. Ironically, this "QWERTY" keyboard layout was originally designed to slow the operator down, so that the keys of the typewriter would not get stuck against each other. This layout now works counter-productively since a computer tin can process keyboard input many times faster than even the fastest typist can manage. A number of attempts have been made to design culling layouts by rearranging the keys (the Dvorak keyboard) or by reducing the number of keys. None of these alternative designs has actually caught on. Special keyboards have besides been designed for countries that use a non-Roman alphabet, and also for disabled people.

Pointing devices

The now ubiquitous electronic mouse is an essential input device for apply with any graphical user interface. Information technology consists of a plastic moulded housing, designed to fit snugly in the palm of the hand, with a small-scale ball at its bottom. Moving the mouse across a flat surface will translate the movements into a rolling action of the brawl. This is translated into electronic signals that direct the corresponding movement of a cursor on the calculator monitor. Buttons on the mouse tin can and so be used to select icons or carte items, or the cursor tin exist used to trace drawings on the screen.

The less popular trackball operates exactly like an "upside-downwards" mouse except that the ball is much larger and, instead of the mouse being moved over a surface, the user manipulates the ball straight. Since the trackball can be built into the side of the keyboard, it obviates the need for a free surface area and is therefore handy in situations where desktop surface expanse is at a premium or not available. Originally pop in educational laboratory settings and for laptop computers, trackballs are now mainly confined to exhibition displays and other public terminals.

Touch-screens are computer monitors that incorporate sensors on the screen panel itself or its sides. The user can bespeak or select an area or location on the screen by pressing a finger onto the monitor. Light and touch pens work on a similar principle, except that a stylus is used, allowing for much finer control. Touch pens are more usually used with handheld computers such as personal organizers or digital assistants. They take a pen-based interface whereby a stylus (a pen without ink) is used on the modest affect-sensitive screen of the handheld reckoner, mainly past means of ticking off pre-defined options, although the fancier models support data entry either past means of a stylized alphabet, which resembles a blazon of shorthand, or some other more sophisticated handwriting recognition interface.

Digitizer tablets also apply a pressure sensitive area with a stylus. This can be used to trace drawings. A similar conceptual approach is used for the bear upon pad that can be institute on the bulk of new notebook computers, replacing the more awkward joystick or trackball. The user controls the cursor by moving a finger across a adequately minor rectangular touch on-sensitive area beneath the keyboard, usually about v cm past 7 cm.

A large number of game interfaces have been developed to provide a more than realistic and natural interface in various gaming situations and simulations: the joy stick, steering wheel, human foot pedal and other gaming devices. They all perform functions similar to the mouse in that they allow the user to control a cursor or simulate generally real-time motility command. Contact your nearest game arcade for details.

Although the data glove also fits under the previous category, it is technically a lot more complex. Information technology looks like a paw glove but contains a large number of sensors and has a data cablevision attached; though the latter is existence replaced past means of infrared cordless information transmission. Not only does the data glove allow for full iii-dimensional movement but information technology also senses the position of individual fingers, translating this into a grip. The glove is currently used in virtual reality simulators where the user moves around in an artificially rendered surroundings projected onto tiny LCD screens fitted into vision goggles. The reckoner generates diverse imaginary objects, which the user can "pick upwards" and manipulate by means of the glove. Advanced models fifty-fifty let for tactile feedback by means of pocket-sized pressure pockets built into the glove.

Optical scanners and readers

There are a number of different optical scanner technologies on the market.

• Optical Scanners use calorie-free-emitting devices to illuminate the printing on paper. Depending on how much light is reflected, a lite-sensor determines the position and darkness (or color) of the markings on the paper. Special-purpose optical scanners are in use past postal services to read and / interpret hand-written postal codes. Full general-purpose scanners are used with personal computers to browse in images or text. These vary from handheld devices (run across picture) to flatbed scanners which feed input documents one sail at a time. A common use of optical scanners is the scanning of blackness-and-white or color images and pictures. When scanning text, it is necessary to load additional optical character recognition (OCR) software that converts the scanned raster-paradigm of the text into the equivalent character symbols, and then that they can be edited using give-and-take processing software.
• Barcode scanners detect sequences of vertical lines of different widths, the ubiquitous barcode as plant also on the back of this book. These scanners accept go very pop with retailers due to the fact that all pre-packaged products are now required to have a product bar code on their packaging, following the standard laid down by the Due south African Article Numbering Clan (SAANA). Libraries and video shops now also usually use bar code scanners. They are more generally used for tracking and routing big numbers of concrete items such as for asset inventory purposes in many larger organizations, postal items by the postal services and courier services, or for luggage handling by airlines.
• Optical marking readers are capable of reading dark marks on specially designed forms. The ruddy multiple option answer sheets in utilize at many educational and testing institutions are a skillful example.

Other input devices

A magnetic card reader reads the magnetized stripe on the dorsum of plastic credit-carte du jour size cards. These cards need to be pre-recorded following sure standards. Although the cards can hold only a tiny corporeality of information, they are very pop for admission (door) control and financial transactions (ATMs and indicate-of-sale terminals).

Magnetic ink character recognition (MICR) uses a special ink (containing magnetizable elements) and a distinct font type. It is used mainly in the cyberbanking sector for the processing of cheques.

Affect-tone devices can utilize a voice telephone to contact computer-based switchboards or enter information directly into remote computers. Many corporate telephone aid-lines rely on the customer pressing the touch-tone telephone buttons to route his/her call to the correct operator by selecting through a menu of possible options. South African banks too enable their clients to perform a number of cyberbanking transactions via telephone.

Digital cameras allow you to make pictures of physical objects directly in a digital, i.eastward. computer-readable, format. Relatively low-cost digital withal picture cameras are now available that capture images directly on electronic disk or RAM media instead of the traditional film. Apart from being very compact, about of these digital cameras can also interface directly with personal computers and are thus becoming a pop tool to capture pictures for due east-mailing or loading on the world-wide Web.

Biometric devices are used to verify personal identity based on fingerprints, iris or retinal scanning, hand geometry, facial characteristics etc. A scanning device is used to capture cardinal measurements and compare them confronting a database of previously stored information. This type of authentication is condign increasingly important in the control of physical access.

Finally, vocalism input devices are coming of age. Voice-recognition has recently made a strong entry into the market with the availability of low-toll systems that piece of work surprisingly well with today'due south personal computers. These systems allow for vocalism control of about standard applications (including the operating system). With voice command, the computer recognizes a very limited number (50 or less) of frequently used, programmable organisation commands ("save", "exit", "print"…) from a variety of users. In fact, these systems are not only used for the interface of figurer programs; they are likewise slowly making an advent in consumer appliances, novelty items and fifty-fifty motor cars!

Much more difficult to attain than vox control, is truthful voice dictation used to dictate e.yard. a letter of the alphabet to your word processor. The difficulty is that the computer must not but distinguish between many tens of thousands of possible words, but it must as well recognize the almost unnoticeable breaks in between words, different accents and intonations. Therefore, vocalism dictation typically requires a user to train the vox recognition software by reading standard texts aloud. Nevertheless, for personal purposes and slow typists, voice recognition is rapidly condign a viable culling to the keyboard.

Primal Processing Unit of measurement (CPU)

Once information has been entered into a estimator, it is acted on by the CPU, which is the real brain of the estimator. The CPU takes specific programme instructions (usually i at a time), applies them to the input data and transforms the input into output.

Components of the CPU

The CPU has two major components.

• The Arithmetic and Logic Unit of measurement (ALU) executes the bodily instructions. It knows how to add together or multiply numbers, compare data, or convert information into unlike internal formats.
• The Control Unit does the "housekeeping" i.east. ensures that the instructions are processed on time, in the proper sequence, and operate on the right data.

Effigy 1: Detailed view of a computer arrangement

Types of CPUs

The CPU is an electronic device based on microchip technology, hence information technology is likewise oft called the microprocessor. Information technology is truly the showcase and culmination of the state-of-the-art in the electronics industry: a tiny silicon-based chip occupying less than 1 square cm contains several millions of transistor elements, measuring less than a thousandth of a millimeter across. They operate at speeds way beyond our comprehension: a typical CPU can multiply more than 7-digit numbers in one second than a human could exercise in ten lifetimes, merely uses less free energy than a light bulb!

Think of the motor auto industry: there are different manufacturers or makes of cars (Volkswagen, Toyota, etc.), each with different models (Golf, Jetta, …), which come out in different versions (City Golf game, Sports model, coupe, etc.). In improver, there exist custom-made special-purpose cars. It is the same in the reckoner bit business. There are many dissimilar types of CPUs on the market. The best-known manufacturer is Intel, which produces the microprocessors for the IBM-compatible personal computer (PC). Some of its competitors produce clones or imitations (e.m. AMD), others manufacturers produce different types of microprocessors or concentrate on small volumes of highly specialized or very fast microprocessors. Intel has produced a large number of CPU types: the earliest model used in the Personal Computer was the 8088, followed past the 8086, the 80286, the 386, 486 and the line of Pentium processors.

Speed of processing

How does ane measure the speed of, say a Porsche 911? One could mensurate the time that it takes to bulldoze a given distance due east.g. the 900 km from Greatcoat Town to Bloemfontein takes iv'/2 hours (ignoring speed limits and traffic jams). Alternatively, one tin can point how far it can be driven in one standard time unit of measurement e.g. the car moves at a cruising speed of 200 km/hour.

In the same mode, one can measure out the speed of the CPU by checking the time it takes to process 1 single instruction. Every bit indicated above, the typical CPU is very fast and an teaching can be washed in virtually 2 billionths of a second. To deal with these minor fractions of time, scientists accept devised smaller units: a millisecond (a thousandth of a 2nd), a microsecond (a millionth), a nanosecond (a billionth) and a picosecond (a trillionth).

However, instead of indicating the time it takes to execute a single instruction, the processing speed is unremarkably indicated by how many instructions (or computations) a CPU can execute in a second. This is exactly the inverse of the previous measure; e.one thousand. if the average instruction takes two billionths of a second (ii nanoseconds) then the CPU tin execute 500 million instructions per 2d (or ane divided by 2 billionths). The CPU is so said to operate at 500 MIPS or 500 million of instructions per 2d. In the globe of personal computers, one commonly refers to the rate at which the CPU can procedure the simplest teaching (i.e. the clock rate). The CPU is and then rated at 500 MHz (megahertz) where mega indicates one thousand thousand and Hertz means "times or cycles per second". For powerful computers, such every bit workstations, mainframes and supercomputers, a more than complex instruction is used as the basis for speed measurements, namely the so-called floating-point operation. Their speed is therefore measured in megaflops (million of floating-betoken operations per 2d) or, in the case of very fast computers, teraflops (billions of flops).

In practice, the speed of a processor is dictated by four unlike elements: the "clock speed", which indicates how many simple instructions tin be executed per second; the word length, which is the number of $.25 that can be processed by the CPU at any one time (64 for a Pentium Four fleck); the bus width, which determines the number of bits that tin can be moved simultaneously in or out of the CPU; then the physical design of the chip, in terms of the layout of its individual transistors. The latest Pentium processor has a clock speed of well-nigh 4 GHz and contains well over 100 meg transistors. Compare this with the clock speed of 5 MHz accomplished past the 8088 processor with 29 000 transistors!

Moore'south Police (see Figure ii) states that processing ability doubles for the same toll approximately every 18 months.

Figure 2. Illustration of Moore's Law

Von Neumann versus Parallel CPU Compages

The traditional model of the reckoner has 1 unmarried CPU to process all the data. This is called the Von Neumann compages because he engineered this approach to computers in the days when computers were all the same a dream.

Except for entry-level personal computers, most computers now have two, four, or up to sixteen CPUs sharing the main processing load, plus various support processors to handle maths processing, communications, disk I/O, graphics or signal processing. In fact many CPU chips at present contain multiple "cores" each representing an private CPU.

Some super-computers that have been designed for massive parallel processing, accept up to 64,000 CPUs. These computers are typically used simply for specialized applications such as atmospheric condition forecasting or fluid modeling. Today'due south supercomputers are mostly clusters (tight networks) of many thousands of individual computers.

Possible Future CPU Technologies

Perhaps the major time to come competitor of the microchip-based microprocessor is optical computing. Although the applied science for developing electronic microchips suggests that CPUs volition proceed to increase in power and speed for at to the lowest degree the next decade or so, the physical limits of the technology are already in sight. Switching from electronic to light pulses offers a number of potential advantages: low-cal (which consists of photons) can travel faster, on narrower paths and does not disperse estrus. In theory, ane can even process different signals (each with a dissimilar light frequency) simultaneously using the same aqueduct. Although the benefits of optical processing technology have already been proven in the areas of information storage (CD-Rom, CD-R) and communication (fibre optics), the more complex all-optical switches required for computing are nonetheless nether development in the enquiry laboratories.

A very experimental alternative to optical and electronic technologies is the organic reckoner. Research indicates that, for sure applications, information technology is possible to let a complex organic molecule act every bit a archaic information processor. Since fifty-fifty a tiny container filled with the appropriate solutions contains many trillions of these molecules, i obtains in effect a hugely parallel reckoner. Although this type of figurer can set on combinatorial problems way beyond the scope of traditional architectures, the principal problem is that the programming of the bio-calculator relies entirely on the bio-chemical properties of the molecules.

Another heady simply currently even so very theoretical development is the possible use of quantum properties as the ground for a new type of figurer architecture. Since breakthrough states can exist in juxtaposition, a register of qubits (a flake value in quantum state) takes on all the possible values simultaneously until it is measured. This could be exploited to speed up extremely parallel algorithms and would touch such areas as encryption, searching and fault-correction. To date, experimental computers with a few qubits have been built only the empirical validation of the actual usefulness of quantum computing still remains an open question.

Main Retention

The function of master retentivity (besides referred to as master memory, chief storage or internal storage) is to provide temporary storage for instructions and data during the execution of a program. Main retentiveness is usually known as RAM, which stands for Random Access Memory. Although microchip-based memory is virtually the only technology used by today's computers, there exist many dissimilar types of memory chips.

Random Admission Memory (RAM)

RAM consists of standard circuit-inscribed silicon microchips that contain many millions of tiny transistors. Very much similar the CPU chips, their applied science follows to the so-called police of Moore, which states that they double in chapters or power (for the same price) every 18 months. A RAM chip hands holds hundreds of Megabytes (million characters). They are frequently pre-soldered in sets on tiny retention excursion boards chosen SIMMS (Unmarried In-line Memory Modules) or DIMMS (Dual …) which slot straight onto the motherboard: the chief excursion board that holds the CPU and other essential electronic elements. The biggest disadvantage of RAM is that its contents are lost whenever the power is switched off.

There are many special types of RAM and new acronyms such every bit EDO RAM, VRAM etc. are being created almost on a monthly basis. Ii important types of RAM are:

• Cache memory is ultra-fast retentivity that operates at the speed of the CPU. Admission to normal RAM is unremarkably slower than the actual operating speed of the CPU. To avoid slowing the CPU downwardly, computers usually incorporate some more expensive, faster cache RAM that sits in between the CPU and RAM. This cache holds the information and programs that are needed immediately past the CPU. Although today'south CPUs already incorporate an amount of cache on the excursion itself, this on-flake cache is usually supplemented by an additional, larger, cache on the motherboard.
• Flash RAM or wink memory consists of special RAM chips on a dissever circuit board within a tiny casing. It fits into custom ports on many notebooks, hand-held computers and digital cameras. Dissimilar normal RAM, flash retention is non-volatile i.e. it holds it contents even without external power, and then it is also useful as a secondary storage device.

Read-Only Memory (ROM)

A small only essential chemical element of whatever reckoner, ROM too consists of electronic memory microchips but, unlike RAM, it does not lose its contents when the power is switched off. Its function is likewise very different from that of RAM. Since it is difficult or incommunicable to change the contents of ROM, information technology is typically used to concur program instructions that are unlikely to modify during the lifetime of the computer. The main application of ROM is to store the then-called boot program: the instructions that the reckoner must follow just after it has been switched on to perform a self-diagnosis and so tell it how load the operating system from secondary storage. ROM fries are also found in many devices which contain programs that are unlikely to alter over a pregnant flow of time, such as telephone switch boards, video recorders or pocket calculators. But like RAM, ROM comes in a number of unlike forms:

• PROM (Programmable Read-Only Memory) is initially empty and can be custom-programmed once simply using special equipment. Loading or programming the contents of ROM is chosen burning the chip since it is the electronic equivalent of blowing tiny transistor fuses inside the bit. Once programmed, ordinary PROMs cannot be modified afterward.
• EPROM (Erasable Programmable Read-Only Memory) is similar PROM just, past using special equipment such as an ultra-violet light gun, the memory contents can be erased and so that the EPROM can be re-programmed.
• EEPROM (Electrically Erasable Programmable Read-Simply Retentiveness) is similar to EPROM merely it can be re-programmed using special electronic pulses rather than ultraviolet light so no special equipment is required.

Secondary Storage Devices

Since the main memory of a reckoner has a limited capacity, information technology is necessary to retain data in secondary storage between different processing cycles. This is the medium used to store the program instructions equally well as the information required for future processing. About secondary storage devices in employ today are based on magnetic or optical technologies.

Disk drives

The deejay drive is the most popular secondary storage device, and is found in both mainframe and microcomputer environments. The cardinal machinery of the disk drive is a flat deejay, coated with a magnetizable substance. As this deejay rotates, data tin can be read from or written to it past means of a head. The head is fixed on an arm and can motility across the radius of the deejay. Each position of the arm corresponds to a "runway" on the disk, which can be visualized equally ane concentric circle of magnetic data. The data on a track is read sequentially as the deejay spins underneath the head. There are quite a few different types of disk drives.

In Winchester hard drives, the disk, access arm and read/write heads are combined in i unmarried sealed module. This unit of measurement is not normally removable, though there are some models bachelor where the unit as a whole can be swapped in and out of a specially designed drive bay. Since the drives are non handled physically, they are less probable to be contaminated by dust and therefore much more than reliable. Mass production and technology advances have brought dramatic improvements in the storage capacity with Terabyte hard drives being land of the art at the end of 2006. Current disk storage costs every bit piffling Rl per gigabyte.

Large organizations such as banks, telcos and life insurance companies, crave huge amounts of storage infinite, frequently in the order of many terabytes (one terabyte is one million megabytes or a trillion characters). This was typically provided by a roomful of large, loftier-capacity difficult drive units. Currently, they are being replaced increasingly past redundant arrays of independent disks (RAIDs). A RAID consists of an independently powered chiffonier that contains a number (10 to 100) of microcomputer Winchester-type drives but functions as one single secondary storage unit. The reward of the RAID is its high-speed access and relatively low cost. In improver, a RAID provides extra data security by means of its fault-tolerant design whereby critical data is mirrored (stored twice on unlike drives) thus providing physical data redundancy. Should a mirrored drive fail, the other drive steps in automatically every bit a backup.

A low-cost, low-chapters version of the hard deejay was popularized by the microcomputer. The diskette consists of a flexible, magnetic ti^J surface coated mylar deejay inside a thin, non-removable, plastic sleeve. The early versions of the diskette were fairly large (8″ or 5W) and had a flexible sleeve, hence the proper noun floppy diskette. These have quickly been replaced past a diskette version in a sturdier sleeve, the stiffy deejay, that despite its smaller size (3 W') can hold more information. Although the popular IBM format simply holds 1,44 megabytes, a number of manufacturers accept developed diskette drives that tin store from 100 to 250 megabytes per stiffy. An alternative development is the removable disk cartridge, which is like in structure to an internal difficult drive but provides portability, making it useful for fill-in purposes.

Magnetic record

While disk and optical storage have overtaken magnetic tape as the virtually popular method of storing data in a computer, record is still used occasionally – in item for keeping archive copies of important files.

The main drawback of magnetic tape is that information technology is not very efficient for accessing data in any way other than strictly sequential order. Equally an illustration, compare a CD player (which can skip to any runway nearly instantly) with a music tape recorder (which has to wind the tape all the fashion through if one wants to listen to a vocal nigh the end). In estimator terms, the ability to admission any tape, rails, or fifty-fifty office within a vocal direct is chosen the direct access method. In the case of the record recorder one may accept to wind laboriously through the tape until one reaches the song required – this is referred to as the sequential admission method.

The high-density diskette and recordable optical deejay have all just eroded the marginal cost advantage that tape storage enjoyed. This technology is therefore disappearing fast.

Optical disk storage

Optical disks, on the other hand, are rapidly becoming the storage medium of choice for the mass distribution of data/programs and the backup of data. Similar to disk storage, information is stored and read from a circular deejay. However, instead of a magnetic read head, a tiny laser axle is used to discover microscopic pits burnt onto a plastic disk coated with reflective material. The pits decide whether near of the light amplification by stimulated emission of radiation light is reflected dorsum or scattered, thus making for a binary "on" or "off". In dissimilarity to difficult disks, information is not stored in concentric cylinders but in 1 long continuous screw runway.

Footling fact: The screw rail used to shop information on a CD is over 6 kilometers long.

A pop optical disk format is the 12-cm CD-ROM. The widespread use of music compact discs has made the engineering very pervasive and inexpensive. Production costs for a CD-ROM are less than Rl, even for relatively small product volumes. The drive reader units themselves have also dropped in price and are now hardly more than the cost of a diskette drive. A standard CD-ROM can store 650 megabytes of data and the data can be transferred at many megabytes per second, though accessing non-sequential data takes much longer.

The CD-ROM is a read-only medium. Data cannot exist recorded onto the disk. The low toll and relatively large chapters makes the CD-ROM ideally suited to the distribution of software. They are also ideal for the depression-cost distribution of large quantities of data such as production catalogues, reference materials, conference proceedings, databases, etc. It is indispensable for the storage of multimedia where traditional textual information is supplemented with audio, music, vocalization, pictures, animation, and even video clips.

The limitation of the read-only format pb to the development of low-cost recordable optical disks. The meaty deejay recordable (CD-R) is a write-in one case, read-many (WORM) technology. The CD-R drive unit of measurement takes a blank optical disk and burns information onto information technology using a higher-powered laser. This disk can then be read and distributed as an ordinary CD-ROM, with the reward that the data is non-volatile i.east. permanent. The rapid driblet in the price of drive units and blank recording media (less than R2 per CD-R) is making this a very competitive engineering for data fill-in and pocket-sized-calibration data distribution.

Although the 650 megabytes initially seemed almost limitless, many multimedia and video applications now crave more storage. A new format, the Digital Video Data (DVD) standard increased the capacity of the CD-ROM past providing high-density, double-sided and double-layered CDs. By combining the increased storage capacity with sophisticated information compression algorithms, a DVD disc tin can easily shop 10 times as much as a CD, sufficient for a total-length high-quality digital flick with many simultaneous audio tracks.

Even the DVD is not sufficient storage capacity and currently two optical technologies have been developed to increase storage capacity fifty-fifty farther. The basic specification of both HD-DVD and Blu-Ray provide for more than than 25 GB of storage on a disc although multi-layer Blu-Ray discs with capacities of more than than 200 GB have already been developed.

A promising research area involves the utilise of holographic disk storage whereby data is stored in a three-dimensional manner. Though in its infancy, early on prototypes promise a many-fold increase in storage chapters and it could become the answer to the ever increment storage requirements of the next decade

Effigy 3: Comparing of secondary storage devices

Device	Access Speed	Capacity	Cost
RAM	< 2 nanosec	256 MB (chip)	<R1/MB
Tape	serial only	500 MB-four GB	<10c/MB
Diskette (3 ane/2″)	300 ms	1,44 MB	R1/MB
PC hard disk	10 ms	xl-750 GB	<2c/MB
M/F hard deejay	25 ms	100+ GB	R2/MB
CD-ROM	<100 ms	660 MB	<0.1c/MB
CD-R	<100 ms	660 MB	<0.2c/MB
DVD	<100 ms	8 GB	<0.1c/MB
Hard disk-DVD	<100 ms	30 GB	?
Blu-Ray	<100 ms	25 GB-200GB	?

Output Devices

The concluding stage of information processing involves the use of output devices to transform computer-readable data back into an data format that can be processed past humans. As with input devices, when deciding on an output device you need to consider what sort of data is to be displayed, and who is intended to receive it.

One stardom that can be drawn between output devices is that of hardcopy versus softcopy devices. Hardcopy devices (printers) produce a tangible and permanent output whereas softcopy devices (display screens) present a temporary, fleeting image.

Display screens

The desk-based computer screen is the most popular output device. The standard monitor works on the same principle as the normal Television tube: a "ray" gun fires electrically charged particles onto a peculiarly coated tube (hence the name Cathode-Ray Tube or CRT). Where the particles hit the coating, the "blanket" is beingness "excited" and emits calorie-free. A stiff magnetic field guides the particle stream to course the text or graphics on your familiar monitor.

CRTs vary substantially in size and resolution. Screen size is usually measured in inches diagonally across from corner to corner and varies from equally little as 12 or xiv inches for standard PCs, to every bit much as 40+ inches for big demonstration and video-conferencing screens. The screen resolution depends on a number of technical factors.

A technology that has received much impetus from the fast-growing laptop and notebook market is the liquid crystal display (LCD). LCDs take matured quickly, increasing in resolution, contrast, and color quality. Their main advantages are lower free energy requirements and their thin, flat size. Although culling technologies are already being explored in research laboratories, they currently dominate the "flat display" market.

Organic lite-emitting diodes (OLED) can generate brighter and faster images than LED engineering science, and require thinner screens, but they accept less stable color characteristics, making them more suitable for cellular telephone displays than for computers.

Another screen-related engineering science is the video projection unit. Originally developed for the projection of video films, the current trend towards more portable LCD-based lightweight projectors is fuelled past the needs of computer-driven public presentations. Today's units fit hands into a small suitcase and project a estimator presentation in very much the same fashion a slide projector shows a slide presentation. They are rapidly replacing the apartment transparent LCD panels that needed to exist placed on top of an overhead projection unit. Though the LCD panels are more meaty, counterbalance less and are much cheaper, their image is generally of much poorer quality and less bright.

Printers and plotters

Printers are the most popular output device for producing permanent, paper-based computer output. Although they are all hardcopy devices, a distinction can be fabricated between impact and not-impact printers. With impact printers, a hammer or needle physically hits an inked ribbon to leave an ink impression of the desired shape on the paper. The advantage of the impact printer is that it can produce more than than 1 simultaneous copy past using carbon or chemically-coated newspaper. Non-touch on printers, on the other paw, take far fewer mechanically moving parts and are therefore much quieter and tend to exist more reliable.

The following are the main types of printers currently in use.

• Dot-matrix printers used to exist the familiar depression-cost printers connected to many personal computers. The print caput consists of a vertical row of needles each of which is individually controlled past a magnet. As the impress head moves horizontally beyond the paper, the individual needles strike the paper (and ribbon in betwixt) equally directed past the control machinery to produce text characters or graphics. A close inspection of a dot-matrix printout volition reveal the elective dots that make up the text. Although it is one of the cheapest printer options, its print quality is generally much lower that that of laser and ink-jet printers. However, today'southward models are quick and give a much better quality by increasing the number of needles.
• Laser printers are rapidly growing in market share. They work on the same principle as the photocopier. A laser beam, toggled on and off very rapidly, illuminates selected areas on a photo-sensitive drum, where the calorie-free is converted into electrical charge. As the drum rotates into a "bed" of carbon particles ("toner") with the opposite charge, these particles will adhere to the drum. The bare paper is so pressed against the pulsate and so that the particles "rub off onto the paper sail. The sheet then passes through a high-temperature area and then that the carbon particles are permanently fused onto the newspaper. Electric current high-finish laser printers tin cope with extremely large printing volumes, equally is required eastward.g. past banks to print their millions of monthly business relationship statements. The light amplification by stimulated emission of radiation technology continues to develop in tandem with photocopier technology. Laser printers can now handle color printing, double-sided printing or combine with mail equipment to perforate, fold, accost and seal automatically into envelopes. At the lower end of the calibration are the low-cost "personal" light amplification by stimulated emission of radiation printers, which give a very good printing quality at a relatively modest toll.
• Thermal printers use rut to print. The older thermal printers used rut-sensitive paper, similar to the special fax newspaper. A slight estrus or pressure level will exit a darker area. This produced very inexpensive but depression-quality output. Currently, thermal-press technology is used mainly for high-quality color printing. These new thermal printers use colored wax sticks and melt the wax onto the paper. Although they are slower than competing colour laser and inkjet technologies, they give a much more vibrant, color-saturated image.
• Inkjet printers are probably the most popular low-cost printing technology. Liquid ink is squirted onto the paper in the form of tiny droplets. These printers are about the aforementioned price as dot-matrix printers, admitting more expensive in terms of consumables. Their quality is close to that of the light amplification by stimulated emission of radiation printers. Their great advantage is that the printers tin can easily be adapted to use coloured ink, thus making popular color printers.
• Plotters are mainly used for applied science and architectural drawings. A plotter consists of one (or several – in the instance of color plotters) pen(s) affixed to an arm. As the arm moves across the sheet of paper, the pen draws lines onto the paper. It is platonic for line drawings such every bit plans, especially in cases where the paper size exceeds that which can be accommodated by the other types of printers.
• Concatenation and line printers are still popular in mainframe environments for the quick production of big volumes of internal printing. The line printer consists of a horizontal, rotating "drum" with 132 cylinders, each containing a full character set. As the 132-column broad paper moves upwards past the drum, a line at a time, each 1 of the 132 hammers on the other side of the paper strikes at the exact moment that the corresponding cylinder "shows" the correct grapheme. The hammer hits the drum (and ink ribbon) and leaves an imprint of the character on the paper. The chain printer works on the same principle, just uses a horizontally rotating chain with engraved characters, instead of a pulsate. Every bit anyone with some working feel in a big system knows, the print quality of these "estimator printouts" is not very loftier.

Effigy 4-4 compares the various output devices in terms of a number of characteristics.

Figure four: Comparison of output devices

Device	Technology	Quality	Speed	Duplicates?	Graphics?	Fonts?	Color?
CRT	softcopy	high	very fast	n/a	aye	yes	yep
LCD	softcopy	off-white	very fast	n/a	yes	yes	yes
Plotter	hardcopy	off-white	slow	no	yeah	aye	yes
Chain/line printer	hardcopy	low	very fast	yes	no	no	no
Laser printer	hardcopy	loftier	fast/fair	no	yes	yeah	yeah
Dot-Matrix printer	hardcopy	off-white	fast/fair	yes	yes	yeah	some
Inkjet printer	hardcopy	good	off-white	no	yeah	aye	yes

Sound-output devices

A type of output that is condign increasingly popular dissimilar types of audio output. is audio output. There are many different types of audio output.

• Sound output is required by near multimedia applications and sophisticated games. The sound carte du jour in many of today'southward personal computers synthesizes audio by drawing from a library of stored sounds, essentially using the same process as found in music keyboards. More avant-garde multimedia workstations are equipped for full stereo multi-aqueduct surround sound and easily surpass many a modern hi-fi system in cabling and speaker complexity.
• MIDI in/output. Modern day music production would be impossible without a vast array of electronic instruments and keyboards. These are typically controlled past a personal figurer by means of Musical Instrument Digital Interface (MIDI), a common standard for linking, decision-making and processing electronic music.
• Spoken communication synthesis is the production of speech-similar output using an artificial voice. Although the lack of intonation still makes the voice audio artificial, the technology is reasonably mature and tin exist found anywhere from talking clocks and luxury cars to automatic responses for telephonic directory enquiries.

Other Output Devices

Many other, extremely specialized input and output devices have been developed. Procedure control, for instance, is a very specialized field but extremely important for automated factories (car manufacturing, canneries), continuous process environments (nuclear plants, refineries) or hazardous places (microbiological inquiry laboratories, space exploration). For these applications, the estimator relies on a multitude of sensors for its inputs: temperatures, speed, pressure, menses rates, weight, position, … These sensor inputs are then candy by the computers, which in plough control directly robot arms and other mechanical devices such every bit cutters, welding equipment, valves, switches, mixers etc.

South African Perspective

A number of automobile manufacturers accept introduced new model vehicles that optionally includes a vehicle safety system that could reduce road deaths and injuries by foreseeing an unavoidable standoff and activating passenger restraint and protection systems before information technology happens. "Pre-crash safe" has three elements:

• A sensor uses millimeter-wave radar to detect vehicles and obstacles on the road ahead.
• An electronic command unit (ECU) determines whether a collision is imminent based on the position, speed and class of the object. If information technology is…
• The seat belts retract to pull the passengers back into their seats and emergency brake assistance pressure is built, prepare for the driver to hit the pedal.

Until now, vehicle rubber devices have only been able to activate after a collision.

The car's radar, Toyota says, works even in rain and snow and is constantly scanning ahead. Newly developed computer software can quickly determine whether a collision is imminent based on the expected form of the host vehicle equally well as the position, speed and expected class of preceding or oncoming vehicles. This could be the solution we need for South Africa's unacceptably high road decease rate – all we need is for every South African driver to be able to afford the new Toyota!

Beyond the Basics

Commercial development is gear up to begin on the side by side generation of retention: the samarium cube. This technology will permit the storage of upwards to one terabyte (m gigabytes) of information in a cubic centimeter of glass. When an extremely short pulse of laser light is applied to a piece of glass containing the rare earth chemical element samarium, a dot around 400 nanometers in diameter becomes luminous, allowing the glass to be used every bit an optical memory. These luminous dots can be spaced 100 nanometers apart, and upwards to 2000 layers of dots can exist stored and read inside a cubic centimeter of glass, producing a three-dimensional storage medium. The pulse of light used to irradiate the cube lasts for only 1000-trillionth of a 2d (a femtosecond), because a longer pulse of light will create estrus that tin can cause the glass to crack.

Exercises

PC specifications

A friend of yours wants to buy a personal estimator for her modest, home-based service business. She wants to utilize industry-standard software to create brochures, do accounts and fiscal calculations and maintain a database of customers, suppliers, products and orders. She copied downward the specifications for a computer that she saw advertised on TV at a competitive price, but she is not certain whether she would actually need all the components, and she doesn't understand all the technical "buzzwords". Every bit a knowledgeable friend, she has asked you

• to explicate in non-technical terms her questions about the diverse components;
• to identify any obviously incorrect specifications that she might have copied downward wrongly from the advertising, and briefly explain why they are wrong.

The following is her specifications sheet:

Specification	Question	Correct?
1.seven GHz Pentium-4	What does "1.7 GHz" mean?
four MB RAM	What is RAM used for?
500 GB Hard Deejay	What sort of things would exist stored on the hard disk?
X50 CD-ROM	Would I use this to make backups? If not, what would I use it for?
32 MB SVGA Graphics menu	What does this practise?
Stiffy bulldoze	Why do I need ane if I have a CD-ROM?
102 keyboard	Should I go any other input devices too?
14" monitor	Is this likely to be a mod apartment screen like y'all get on laptops, or the old fashioned sort of monitor?
Colour inkjet printer	Why not go a dot-matrix printer?

Input/Output devices

A standard Automated Teller Machine ("ATM") has a large number of input and output devices. List as many of its I/O devices as you lot tin (you may include sensors also).

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