The Standard Keyboard Layout

Keyboards for personal computers come in many styles. the various models differ in size, shape and feel, but except for a few special - purpose keys , most keyboards are laid out almost identically. Among IBM - compatible computers, the most common keyboard layout is the IBM Enhanced keyboard. It has 101 keys arranged in five groups as shown in the figure.The keyboard layout is close to the IBM Enhanced keyboard, but there are a few differences.

The Alphanumeric keys:
The alphanumeric keys - the parts of the keyboard that look like a typewriter - arrange the same way on almost every keyboard, Some times this common arrangement is called QWERTY layout because the first six keys on the top row of letters are Q,W,E,R,T and Y.
For decades, many expert typists have supported a different arrangement for alphanumeric keys called the DVORAK keyboard. This keyboard layout places the most commonly used letters in the middle row of keys, making them easier to reach. Special DVORAK keyboards are available for computer system but they are not standard equipment. A few keyboards manufacturers now offer keyboards that can be switched from QWERTY to DVORAK configurations.

Along with the keys that produce letters and numbers , the alphanumeric key group includes a few additional keys, with specific functions. these keys are similar to those found on a typewriter:

* Tab - The Tab key moves you to predefined tab stops in many application programs. In dialog boxes.you can press tab to move from one option or field to another.

* caps Lock  - As the name implies this key lets you "lock" the alphabet keys so they produce only capital letters. Caps lock does not affect the numeric keys or the keys that produce punctuation or special characters.

* Back Space - This key enables you to erase characters you have just typed for example in a word processing program you can press Backspace to "back over" an incorrect  character and delete it.

* Enter - The Enter key lets you finalize data entry in many types of the application programs . you can also use enter to choose commands and options in many programs and at various places in an operating systems interface.

The Modifier keys:


A keyboard's modifier keys are no named because they are used to modify the input of other keys. You press
another key while holding down one of the modifier keys are as follows:

* shift - A computers shift keys have the same function as a typewriters shift  keys; when pressed in conjunction with an alphanumeric key , shift forces the computer to output a capital letter or symbol. Shift also acts as a modifier key on some programs. In most word processors you can press shift along with various cursor movement keys to select text for editing.

* Ctrl - This key produces different results depending on the program you are using. In many windows based
programs, ctrl - key  combinations provide shortcuts for menu commands. For example , the crtl key combination  ctrl +o enables you to open a new file.

* Alt - this key called the alternative key operates like that control key.except that it produces different set of results. In windows based programs, Alt -key combination enable you to navigate menus and dialog boxes without using a mouse.

Standard methods of keyboard

Overview: Keyboard and the mouse:
If the CPU is the brain of the computer, then the input devices are its eyes and ears. From the users point of view, input devices are just as important as CPU - more so , in fact . After you have purchased and setup the computer, you can take the CPU for granted because you interact directly with the input devices and only indirectly with the CPU. Your ability to use input devices is critical to your overall success with the whole system.

An input device does exactly what its name suggests: it enables you to input information and commands into the computer. the most commonly used input  devices are the keyboard and mouse. In fact if you buy a new personal computer today it will include a keyword and mouse . It will include a keyboard and mouse unless you specify otherwise. As you will see, many other types of input devices are available, including variations of the mouse and specialized "alternative" input devices such as microphones and scanners.

the keyboard was one of the first peripherals to be used with computers and it is still the primary input device for entering text and numbers. A relatively simple device, a standard keyboard includes about 100keys, each of which sends a different signal to the CPU.

If you have not used a computer keyboard or type writer, you will learn quickly that you can use a computer much more effectively if you know how to type.the skill of typing or keyboarding, as it is often called today, implies the ability to enter text by using all ten fingers and without being able to type , and many people do. some people claim that when computers can understand hand writing and speech, typing will become unnecessary. But for now and the foreseeable future, keyboarding remains the most common way to enter text and other data into a computer

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Handheld personal computers

Since the mid 1990s, many new types of small personal computing devices have been introduced . and all fall under the category of  handheld personal computers. these tiny systems are also called palmtop computers, a handheld  Pc can be any sort of computer that fits in the user's hand, such as

1. Personal digital assistant
2. Cellular telephone with internet , email and fax capabilities.
3. H/PC Pro device

some of the handheld personal computers look like  mininotepad computers with small displays and keyboards, but are much smaller than even the tiniest full-featured notebook PC.This type of H/PC is sometimes called a mini - notebook computer. Most H/PC systems do not provide disks, but memory can be added  through PC cards or other means. software is abundant for these devices , most of which are internet - capable and can connect yo a full- size computer to exchange data.

Personal digital Assistants:

Personal digital assistants are among the smallest of portable computers, often they are no larger than a small appointment book, but they are much less powerful than notebook or desktop computers. PDAs are normally used for special applications, such as taking notes, displaying telephone numbers and addresses, and keeping track of dates or agendas. Many PDAs can be connected to larger computers to exchange data.

Most PDAs come with an electronic pen that lets the user write on a touch sensitive screen.
Even  though they do not include real keyboards, some of these devices provide a graphical keyboard  that appears on the screen . you type by tapping the desired keys with the units pen. Depending on the model, PDAs may include the following features:

1. Built in micro phone and speaker , enabling the user to record speech digitally.
2. Personal information management (PIM) software.
3. Miniaturized versions of personal productivity applications.
4. Internet , fax, or email software.

Cellular phones

Some new cellular phones are doubling as miniature PCs. advanced cellular devices combine analog and digital cell phone service with email capabilities. Such phones enable the user to check and send email and faxes over the phone. they offer features not normally found on a phone, such as personal organizers or access to the web. Some models even break in half to reveal a miniature keyboard.

H/PC Devices:

Probably the most curious new development in handheld technology is the  H?PC Pro family of devices. these systems are larger than PDAs or  miniature notebooks, but they are not quite as large as typical notebook PCs, with features some where between the two. for  example , H/PC Pro systems boast nearly full sized keyboards and color displays . they can run more types of miniaturized applications than their smaller counterparts, but those applications still do not provide the features of normal desktop software. H/PC Pro units offer long battery life and instant - on access but they  do not include disks. although they will gain speed and storage capacity quickly, H/ PC Pro systems offer very limited RAM and relatively slow processor speeds.

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Network computers

In some situations user does not need all the power and features provided by personal computer. If you want to use only the internet, for example  or if your job involves data entry, then you may need the processing power , memory, and storage capacity of a fully equipped PC. In this instance a network computer becomes useful.

A network computer is a less powerful version of a personal computer, with minimal processing power, memory and storage. Network computers are designed to be connected to a network , a corporate intranet, or to the internet. The NC relies on the network for software and data storage and may even use the network's server to perform some processing tasks.

In the mid 1990s, the concept of network computers became popular among some PC manufacturers, who pronounced the NC as the future of computing. However, no single NC standard emerged as various hardware and software makers fought to command this new market. As a result , several variations on the network  computer quickly became available and consumers almost immediately became confused about their differences and special purposes. while network computers have gained some market share in business, they have not succeeded to the extent their makers anticipated.

In business, variations of the network computer are thin clients, diskless workstations, windows terminals and Net PCs. Some network computers are designed to be connected only to the Internet boxes, Internet appliances, or step - top boxes. In home settings, some network computers do not even include a monitor; instead, they connect to the user television , which serves as the out put device.

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Notebook computers or laptop computers

Notebook computers , as their name implies approximate the shape of an 8.5 by 11 inch notebook and can fit inside a briefcase easily. Also called  Laptop computers, they can operate in alternating  current or special batteries.Notebooks are fully functional microcomputers; the people who use them need the power of a full - size PC wherever they go.

Some notebook systems are designed to be plugged into a docking station which may include a large monitor, a full-size keyboard and mouse, or other devices such as an additional hard drive or backup tape unit. Docking stations also provide additional ports that enable the notebook computers to be connected to different devices in the same manner as desktop system. Some expansion bases also feature built in networking curds so one is not required in the notebook computers.

Because of their size , notebook computers often feature a smaller display, less memory and less storage space than a full size PCs. Also because their size, notebook computers tend to be more expensive than computers. Depending on its features, a fully equipped notebook computer can cost between $500 and $5000.

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Desktop Models

The First style of personal computer introduced was the desktop model. In common usage , the term desktop system means a full size computer that is small enough to be used at a desk but too big to carry around. Traditionally a desktop computer's main case is horizontally oriented, meaning it can lie flat on a desk or table.

A variation of the desktop system is the tower model. where the system unit sits vertically and has more vertically and has more space for devices. Because of its design, the system unit is often placed in the floor to preserve desk space, allowing more room to place external components, such as removable disk drives or scanners, on the desktop.

Tower models have become increasingly popular in recent years - so much so that some PC makers have stopped offering horizontally oriented desktop system.

Personal computers can cost anywhere from $600 to $7500, depending on the capabilities and capacity. The most popular models cost between $1000 and $3000. The tremendous growth and potenial of the pc market has brought many manufactures into this arena.

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types of mini computers

The minicomputers category has grown tremendously in the past decade. There are now several specific types of microcomputers, each with its own capabilities features and purposes. with in each subcategory of microcomputer, you can find computer " the computer for the masses" and explains why so many systems have appeared in offices, homes, brief cases and even pockets iver the past few years.

Microcomputers include the following types.
1. Desktop models, including tower models.
2. Notebook computers also called laptop computers.
3.Network computers.
4. Handheld personal computers of all types.

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Micro computer or Personal computers

The terms microcomputer and personal computer are interchangable,  but PC which stands for personal computer- sometimes has a more specific meaning . In 1981. IBM called its first microcomputer the IBM - PC . Within a few years,Many companies  were copying the IBM design, creating "clone" or "compatibles" that were meant to function like the original. For this reason, the term PC has come to mean the family of computers that includes IBMs and IBM- compatibles . The vast majority  of micro computers sold today are part of this family. The Apple Macintosh computer, however, is neither an IBM compatible. It is another family of microcomputers, made by Apple computer. So it is accurate to say that a Macintosh such as the iMac is a personal computer. Even so , some people consider it misleading to refer to the "Mac" as a PC. this book uses the term PC as a simple abbreviation for personal computer, referring to both IBM - compatible models and Apple's Macintosh line.

One source of the  Pc's Popularity is the rate at which improvements are made in its technology. Microprocessors, memory chips, and storage devices make continual gain in speed and capacity, while physical size and price remain stable or some cases are reduced. For example compared to the typical PC of ten years ago, machine of the same price today will have about ten times as much RAM, about 100times more storage capacity, and a microprocessor at least100 times as fast. What's more , many analysts believe that this pace of change will continue for another 10 to 20 years.

One result of increasing Pc power is that the differences among mainframes, minis and microcomputers are not as great as they once were. In fact , the processing power of PC's often rivals that of current  mainframes are still popular because they can handle the input and output needs of many users at once, so  they are still the right choice for the  massive databases that many people need to systems is their reliability. Mainframes are known for their robustness and ability to handle tremendous loads without failing.

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Work Stations

Some where between multi user midrange computers and personal computers are workstations. work stations are specialized , single user computers with many of the features of  a personal  computer but with the processing power of a mini computer. These powerful machines are popular among scientists, engineers, graphic artists, animations and programmers. users who need a great deal of number crunching power. Workstations typically use advanced processors and feature more RAM and storage capacity than personal computers. Work stations often have large , high - resolution monitors and accelerated graphics - handling  capabilities , making them perfect for advanced design, modeling, animation and video editing. Although workstations are often found in single - user applications, they are more and more often used as servers on personal computers networks and as web servers.

Until a few years ago, the term workstation implied certain differences in terms of chip design and operating system, making it distinct from a personal  computers. Today, the differences between minicomputers, workstations and personal computers are becoming blurred. Low end minicomputers and high end workstations are now similar in features and capabilities. the same is true for low end workstations and high end personal computers.

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Mini computers

First released in the 1960's . mini computers got their name because of their small size compared to other computers of the day. the capabilities of a minicomputer are some where between mainframes and personal computers. Like main frames , mini computers can handle much more input and output  than personal computers can. although some "minis" are designed for a single user, most are designed to handle multiple terminals. the most powerful minicomputers can serve the input and output needs of hundreds of users at a time.

Mini computers, such as the one shown in the figure above. are commonly used as servers in the network environments that handle  the data sharing needs of other computers on the network . dozens or hundreds of personal computers can be connected to a network with a minicomputers acting as a server. Like mainframes, midrange computers are used more and more as web servers, handling thousands of transactions per day. single - user mini computers are commonly applied to sophisticated design tasks, such as animation and video editing. Mini computers cost  anywhere from $18000 to $500,000 and are ideal for many organizations and compies that cannot afford or do not need a mainframe system.

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Main Frame computers

The Largest type of computer in common use is the mainframe. Main frame computers are used in large organizations like insurance companies and banks where many people need frequent access to the same data, which is usually organized into one or more huge data bases.

    Air lines use large mainframe systems for flight scheduling , reservations, ticketing and meeting a range of customer service. Federal aviation Administration and the census Bureau - use mainframes to tract information   

about large populations, individual tax records, payroll and more. Many large  grocery and retail chains interconnected their stores with a mainframe, which immediately registers every sale , oversees stock and manages inventory levels.

Mainframes are being used more and more as specialized servers on the world wide web,enabling companies to offer secure transactions with customers over the internet. If you purchase an air line ticker over the web, for example , there is a good chance your transaction is being is being handled by mainframe system. In this type of application , the mainframe system may referred to as an enterprise server or an electronic commerce server.

In a transitional mainframe environment , each user works at a computer terminal. A terminal is a monitor and a keyboard  wired to the mainframe. There are basically two types of terminal used with mainframe systems. A dumb terminal does not have its own CPU or storage devices. these components are housed in the mainframe's system unit and are shared by all users. Each dumb terminal is simply an input/output (I/O) device that functions as a window into a computer located somewhere else. An intelligent  terminal, on the other hand , has its own processor and can perform some processing operations. Intelligent terminals, however, do not usually provide any storage.

Many enterprises are now connection personal computer networks to their mainframe system. This connection gives users access to mainframe data and services and also enables them to take advantages of local storage and processing, as well as other features of the PC or network.

A mainframe system can house an enormous volume of data, containing literally billions of records. Large mainframe systems can handle the input and output requirements of several thousand terminals. the largest IBM S/390 mainframe, for example , can support 50,000 users simultaneously while executing more than 1,600,000,000 instructions per second.

Depending on their size, capabilities and the number of users they must support, mainframe systems can cover a huge price range . Mainframe systems start at around $30,000; extensive mainframes can several million dollars.

If used to be common for mainframe computers  to occupy entire rooms or even an entire floor a high rise building. Typically, they were placed inside glass offices with special air conditioning to keep them cool and on raised floors to accommodate all the wiring needed to connect the system. This setup is not unimposing file cabinet - or row of file cabinets - although it may still require a some what controlled environment.

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SuperComputers

Supercomputers are the most powerful computers made and physically they some of the largest. These systems are built to process huge amount of data and the faster supercomputers can perform more than 1 trillion calculations per second. some supercomputers - such as the Cray'T90 system -can house thousands of processors. This speed and power make supercomputers ideal for handling large and highly complex problems that require extreme calculating power.

Scientist and engineers frequently build models of complex processes, then simulate the processes on a supercomputer. These computers help analyze and forecast global weather patterns, for example, while shedding light on related issues such as pollution, global warming and the depletion of the earth's ozone layer. Nuclear scientist use supercomputers to create and analyze models of nuclear fission and fusion, predicting the actions and reactions of millions of atoms as they interact.

Supercomputers are also being used to map the human genome, or DNA structure. The Human Genome project, for example, uses supercomputing resources around the world in the hope of discovering all the human genes. scientist estimate there are from 80,000 to 100,000 human genes, made up of more than 3 billion chemical bases. If printed, th ehuman DNA sequence would fill about 200,000pages.

Supercomputers can cost tens of millions of dollars and consume enough electricity to power dozens of homes. They are often housed in protective rooms with special cooling systems, power protection, and other security features . Because of their size and cost , supercomputers are relatively used only by large corporations, universities and government agencies that can afford them. Supercomputing resources are often shared to give researchers access to these precious machines.

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The types of computer

Computers come in many different sizes and ranges of power and different types of computer systems have varying capabilities. Basically , today's computer system fall into one of the following categories.

1.Supercomputers.
2.Mainframe computers
3.Minicomputers or mid range computers
4.Workstations
5.Microcomputers or personal computers

All of these computers can be connected to form networks of computers, but each individual computer, whether or not it is on a network, falls into one of these categories - especially microcomputers can be divided into subcategories, some of which are growing  rapidly enough to become major categories in their own right.

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Operating system

When you turn on computer, it goes through several steps to prepare itself for use. the first is called  the Power on self test(POST). The computer identifies the devices attached to it, identifies the amount of memory available and does quick check to see whether the memory is functioning properly. This routine  is initiated by a part of the system software located in read-only memory(ROM), a chip that contains brief, permanent instructions for starting the computer.

Next, the computer looks for an operating system, which is usually stored in the hard disk. The operating system tells the computer how to interact with the user and how to use devices such as the disk drives, keyword, and monitor. When it finds the operations, the computer loads a portion of it into memory. Because the operating system is necessary for controlling the computers most basic functions, it continues to run until the computer is turned off.

After the computer finds and runs the operating system, it is ready to accept commands from an input device - usually the keyboard or a mouse - or from a program. At this point , the user can issue commands to the computer. A command might , for example, list the programs stored on the computers disk or make the computer run one of those programs.

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Storage in Computer

A computer can function with only processing , memory, input and output devices. To be really useful, however, it also needs a place to keep program files and related data when it is not using them. The purpose of storage is to hold data. 

Think of storage as an electronic file cabinet and RAM as an electronic workable. when you need to work with a program or a set of data, the computer locate it in the file cabinet and puts a copy on the table. After you have finished working with the proram or data, you put it back into the file cabinet. If you make changes to data while working on it, the changed data replaces the original data in the file cabinet .

There are three major distinctions between storage and memory:

1. There is more room in storage than in memory , just as there is more room in a file cabinet than there is on a tabletop.

2. Contents are retained in storage when the computer is turned off, whereas the programs or the data you put into memory disappear when you shutdown the computer.

3. Storage is very slow compared to memory, but it much cheaper than memory.

Remember the distinction between storage and memory. Their functions are similar, but they work in different ways. Novice computer users often use the term memory when they actually mean storage or disk. This mistake can cause confusion.

The most common storage medium is the magnetic disk. A disk is a round, flat object that spins around its center. Read/write heads, which are similar to the heads of a tape recorder or VCR, are used to read data from the disk or write data onto the disk, Depending on the type of disk , the read/write heads may float just above the disk's surface or may actually touch the disk.

The device that holds a disk is called disk drive. Some disks are built into the drive and are not meant to be removed ; other kinds of drives enable you to remove  and replace disks. Most personal computers have at least one non removable hard disk. In addition, there is also a diskette drive, which allows you to use removable disk or hard drive. In addition , there is also a diskette drive, which allows you to use removable diskettes. A hard disk can store far more data than a diskette can, so the hard disk serves as the computer's primary filing cabinet. Diskettes are used to load new programs or data onto the hard disk , trade data with other users , and make backup copies of the data on the hard disk.

Because you can remove diskettes from a computer from a computer, they are encased in a plastic or vinylcover to protect them from fingerprints and dust. Because the cover used in early diskettes was thin, the diskette was flimsy or "floppy" as a result they came to be called floppy disk.

The CD - ROM drive is the most common type of storage device after the hard and diskette drives . Compact disks are a type of optical storage device, identical to audio. CDs, that can store about 74 minutes of audio or 650 MB of data, or about 450 times as much information as a diskette. The type used in computers is called Compact Disk Read - Only Memory (CD-ROM). The name implies that you cannot change information on the disk, just as you cannot record over an audio CD.

If you purchase a CD-Recordable (CD-R) drive, you have the option of creating your own CDs. A CD-R drive can write data to and read data from compact disk. To use CD-Drive, you must use a special CD-R disk, which can be written on only once, or a CD- Rewrite-able (CD-RW)disk, which can be written to multiple times, like a floppy disk.

                                                                  CD - Recordable

An increasingly popular storage technology is the digital versatile disk or  Digital Video Disk (DVD) , which is revolutionizing home entertainment. Using sophisticated compression technologies, a single DVD which is the same size as a standard compact disk can store an entire fill length movie. DVDs can hold a minimum of 4.7GB of data and as much as 17GB. Future DVD technologies promise much higher storage capacities on a  single disk. DVD drives  can also locate data on the disk much faster than standard CD-ROM drives.

DVDs require  a special player. The new players, however, can play audio, data and DVD disks, freeing the user from the necessity of purchasing different players for each type of disk. DVD drives are now standard  equipment on many new personal computers. Users not only install programs and data from their standard CDs , but they can also watch movies on their PC's by using a DVD.

                                                                              DVD

Other types of storage devices include tape drives, optical drives, removable hard drives, and many others.

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