computer hardware

What is Hardware?

Your PC (Personal Computer) is a system, consisting of many components. Some of those components, like Windows XP, and all your other programs, are software. The stuff you can actually see and touch, and would likely break if you threw it out a fifth-story window, is hardware.

Not everybody has exactly the same hardware. But those of you who have a desktop system, like the example shown in Figure 1, probably have most of the components shown in that same figure. Those of you with notebook computers probably have most of the same components. Only in your case the components are all integrated into a single book-sized portable unit.

Figure 1

The system unit is the actual computer; everything else is called a peripheral device. Your computer's system unit probably has at least one floppy disk drive, and one CD or DVD drive, into which you can insert floppy disks and CDs. There's another disk drive, called the hard disk inside the system unit, as shown in Figure 2. You can't remove that disk, or even see it. But it's there. And everything that's currently "in your computer" is actually stored on that hard disk. (We know this because there is no place else inside the computer where you can store information!).

Figure 2

The floppy drive and CD drive are often referred to as drives with removable media or removable drives for short, because you can remove whatever disk is currently in the drive, and replace it with another. Your computer's hard disk can store as much information as tens of thousands of floppy disks, so don't worry about running out of space on your hard disk any time soon. As a rule, you want to store everything you create or download on your hard disk. Use the floppy disks and CDs to send copies of files through the mail, or to make backup copies of important items.

Random Access Memory (RAM)

There's too much "stuff" on your computer's hard disk to use it all at the same time. During the average session sitting at the computer, you'll probably use only a small amount of all that's available. The stuff you're working with at any given moment is stored in random access memory (often abbreviated RAM, and often called simply "memory"). The advantage using RAM to store whatever you're working on at the moment is that RAM is very fast. Much faster than any disk. For you, "fast" translates to less time waiting and more time being productive.

So if RAM is so fast, why not put everything in it? Why have a hard disk at all? The answer to that lies in the fact that RAM is volatile. As soon as the computer is shut off, whether intentionally or by an accidental power outage, every thing in RAM disappears, just as quickly as a light bulb goes out when the plug is pulled. So you don't want to rely on RAM to hold everything. A disk, on the other hand, holds its information whether the power is on or off.

The Hard Disk

All of the information that's "in your computer", so to speak, is stored on your computer's hard disk. You never see that actual hard disk because it's sealed inside a special housing and needs to stay that way. Unlike RAM, which is volatile, the hard disk can hold information forever -- with or without electricity. Most modern hard disks have tens of billions of bytes of storage space on them. Which, in English, means that you can create, save, and download files for months or years without using up all the storage space it provides.

In the unlikely event that you do manage to fill up your hard disk, Windows will start showing a little message on the screen that reads "You are running low on disk space" well in advance of any problems.  In fact, if that message appears, it won't until you're down to about 800 MB of free space. And 800 MB of empty space is equal to about 600 blank floppy disks. That's still plenty of room!

The Mouse

Obviously you know how to use your mouse, since you must have used it to get here. But let's take a look at the facts and buzzwords anyway. Your mouse probably has at least two buttons on it. The button on the left is called the primary mouse button, the button on the right is called the secondary mouse button or just the right mouse button. I'll just refer to them as the left and right mouse buttons. Many mice have a small wheel between the two mouse buttons, as illustrated in Figure 3.

Figure 3
 

The idea is to rest your hand comfortably on the mouse, with your index finger touching (but not pressing on) the left mouse button. Then, as you move the mouse, the mouse pointer (the little arrow on the screen) moves in the same direction. When moving the mouse, try to keep the buttons aimed toward the monitor -- don't "twist" the mouse as that just makes it all the harder to control the position of the mouse pointer.

If you find yourself reaching too far to get the mouse pointer where you want it to be on the screen, just pick up the mouse, move it to where it's comfortable to hold it, and place it back down on the mousepad or desk. The buzzwords that describe how you use the mouse are as follows:

• Point: To point to an item means to move the mouse pointer so that it's touching the item.
• Click: Point to the item, then tap (press and release) the left mouse button.
• Double-click: Point to the item, and tap the left mouse button twice in rapid succession - click-click as fast as you can.
• Right-click: Point to the item, then tap the mouse button on the right.
• Drag: Point to an item, then hold down the left mouse button as you move the mouse. To drop the item, release the left mouse button.
• Right-drag: Point to an item, then hold down the right mouse button as you move the mouse. To drop the item, release the right mouse button.

The Keyboard

Like the mouse, the keyboard is a means of interacting with your computer. You really only need to use the keyboard when you're typing text. Most of the keys on the keyboard are laid out like the keys on a typewriter. But there are some special keys like Esc (Escape), Ctrl (Control), and Alt (Alternate). There are also some keys across the top of the keyboard labeled F1, F2, F3, and so forth. Those are called the function keys, and the exact role they play depends on which program you happen to be using at the moment.

Most keyboards also have a numeric keypad with the keys laid out like the keys on a typical adding machine. If you're accustomed to using an adding machine, you might want to use the numeric keypad, rather than the numbers across the top of the keyboard, to type numbers. It doesn't really matter which keys you use. The numeric keypad is just there as a convenience to people who are accustomed to adding machines.

Figure 4

Most keyboards also contain a set of navigation keys. You can use the navigation keys to move around around through text on the screen. The navigation keys won't move the mouse pointer. Only the mouse moves the mouse pointer.

On smaller keyboards where space is limited, such as on a notebook computer, the navigation keys and numeric keypad might be one in the same. There will be a Num Lock key on the keypad. When the Num Lock key is "on", the numeric keypad keys type numbers. When the Num Lock key is "off", the navigation keys come into play. The Num Lock key acts as a toggle. Which is to say, when you tap it, it switches to the opposite state. For example, if Num Lock is on, tapping that key turns it off. If Num Lock is off, tapping that key turns Num Lock on.

Combination Keystrokes (Shortcut keys)

Those mysterious Ctrl and Alt keys are often used in combination with other keys to perform some task. We often refer to these combination keystrokes as shortcut keys, because they provide an alternative to using the mouse to select menu options in programs. Shortcut keys are always expressed as:

key1+key2

where the idea is to hold down key1, tap key2, then release key1. For example, to press Ctrl+Esc hold down the Ctrl key (usually with your pinkie), tap the Esc key, then release the Ctrl key. To press Alt+F you hold down the Alt key, tap the letter F, then release the Alt key.

personal area network

Wireless PAN

A wireless personal area network (WPAN) is a personal area network - a network for interconnecting devices centered around an individual person's workspace - in which the connections are wireless. Typically, a wireless personal area network uses some technology that permits communication within about 10 metres (33 ft) such as Bluetooth, which was used as the basis for a new standard, IEEE 802.15.

A WPAN could serve to interconnect all the ordinary computing and communicating devices that many people have on their desk or carry with them today - or it could serve a more specialized purpose such as allowing the surgeon and other team members to communicate during an operation.

A key concept in WPAN technology is known as "plugging in". In the ideal scenario, when any two WPAN-equipped devices come into close proximity (within several meters of each other) or within a few kilometers of a central server, they can communicate as if connected by a cable. Another important feature is the ability of each device to lock out other devices selectively, preventing needless interference or unauthorized access to information.

The technology for WPANs is in its infancy and is undergoing rapid development. Proposed operating frequencies are around 2.4 GHz in digital modes. The objective is to facilitate seamless operation among home or business devices and systems. Every device in a WPAN will be able to plug in to any other device in the same WPAN, provided they are within physical range of one another. In addition, WPANs worldwide will be interconnected. Thus, for example, an archeologist on site in Greece might use a PDA to directly access databases at theUniversity of Minnesota in Minneapolis, and to transmit findings to that database.

[edit]Connecting devices

Connecting devices allow hardware networking devices to communicate with each other. The three kinds of wireless technologies areBluetooth, infrared, and Wireless Fidelity (WiFi).

[edit]Bluetooth

Bluetooth uses short-range radio waves over distances up to approximately 10 metres. For example, Bluetooth devices such as a keyboards, pointing devices, audio head sets, printers may connect to Personal digital assistants (PDAs), cell phones, or computers wirelessly.

[edit]Infrared

Infrared communications (IR) or IrDA (Infrared Data Association) uses infrared light, which has a frequency below the human eye's sensitivity. It is used in cell phones and TV remote controls. Typical devices include printers, keyboards, and other serial data interfaces.^[1]

[edit]WiFi

WiFi (wireless fidelity) uses radio waves for connection over distances up to around 91 metres, usually in a local area network (LAN) environment. Wifi can be used to connect local area networks, to connect cellphones to the Internet to download music and other multimedia, to allow PC multimedia content to be stream to the TV (Wireless Multimedia Adapter), and to connect video game consoles to their networks (Nintendo WiFi Connection).

type of computer network tropology

What is a Network topology

A topology – is the characteristic of a communication network that is concern both with the physical configuration of the cabling that is used to inter connect communicating system and the logical way in which system view the structure of the network. Topology is the therefore physical or logical arrangement of computers

Factors to consider when selecting a topology

1. Cost – whatever transmission medium is chosen for a Local Area Network has to be physically installed in the building, this maybe a lengthy process including the installation cables and raceways. For a Network to be cost effective one would strive to minimize installation cost. This may be achieved by using the proper hardware linking the cables, good modems, cost effective computers to reduced cost
2. Flexibility – one of the main benefit of a local Area Network is it ability to have the data processing and peripheral nodes distributed around a given area. This means that the computing power and equipment can be located close to the ultimate users. Because the arrangements of furniture, internal walls etc in the offices is often subject to change. The topology should allow for easy reconstruction of the network which involves moving existing nodes and adding new nodes
3. Reliability – The topology chosen for the network can help by allowing the location of the fault to be detected and to provide some means of isolating the faults

Diagramatic explanation of star topology

Types of Network Topologies

Network star topology also known as Radial topology

This topology consist of a central nodes to which all other nodes are connected, star topology is used in most existing information network involving data processing and voice communication. In many cases when a building is wired with a star topology, faced cables radiate out from the centre to intermediate connection point to wiring cables. This allows sufficient connection point to be provided for one sub – area, while providing flexibility in their allocation within that area

Advantages of star topology

• Diagnostic and isolation of problem is easy
• Easy to add a new computer system to the network
• Failure of one workstation does not affect the entire network
• Uses a single access protocols
• Provide ease of service
• Is very fast

Disadvantages of star topology

• There is central node dependency
• Becomes expensive when purchasing the nodes
• Always requires very long cable length when connecting many nodes

bus topology diagram

Bus Topology also known as Linear Topology

It is the simplest method of networking computers. It consists of a single cable known as a trunk, backbone or segment that connects all the computers in the network. Each system is directly attached to a common communication channel. Signal that is transmitted over the channel makes up the messages.  As each message passes along the channel each system receives it, after receiving the message each system examine the destination address contained in the message, if the destination address tells a particular system that the message is addressed to it, that system accepts and process the message, if the message address tells the computer that the message is intended for another system, that computer will ignore the message

On a bus topology signals are send to all the computers in the network to keep the signal from bouncing back and forth along the cable a terminator (British Naval Connector) is placed at the end of the cable. In a bus topology only one computer can send data at a time, therefore the more computers in a bus the slower data transmission in the network

Advantages of Bus topology

• Cheap because of its simplicity
• Requires a short cable length
• Easy to expand the network
• Simple to setup compared to Star and Ring topology
• There is no chances of data collision since one computer transmit at a time
• Locating cable fault in a bus topology is relatively easy
• Bus topology is ideal for one to many data transmission
• Signal on the cable are bidirectional hence reaches all the nodes

Disadvantages of Bus topology

·         Fault diagnosis is difficult in a bus topology – detection of fault may have to be performed from any point in the network

·         Fault isolation is difficult – if fault in the node is detected  the node can simply be removed but if the fault is in network medium itself and entire segment of the Bus must be disconnected to isolate the fault

·         Repeater configuration – When a Bus type  network has its backbone intended for using a repeater, configuration maybe necessary thus may involve tailoring cable length, adjusting terminator etc

·         Computer nodes must be intelligence – each node on the network is directly connected to the central Bus. This means that each node must have method of deciding and detecting its own data

Ring topology diagram

Ring Topology

In Ring topology each node is connected to form a single, closed data path. Data from one node is passed along to the next node from which it will be examined, and if that node is not the intended destination, then it is transmitted to the next node until the destination is reached. Token ( a special bit pattern) is circulated in the network to enable a node to capture the data. Ring topology might be structured so that there are a number of information frames or slot in construct circulation. Node wishing to transmit first detects the arrival of an empty slot then inserts the data it wishes to send, and mark the frame as full. The receiving node takes the data and then marks the frame as empty. In implementation one particular node has the responsibility for generating the token or slot when the network is first constituted

Advantages of ring Topology

• The ability to achieve transmission rates of the order of 10 million bits per second
• Provision of local communication via a single channel
• No central server which reduces the cost of establishing the ring topology

Disadvantages

·         Failure of one node result into entire network failure

·         Detection of fault is very difficult in ring topology

·         Isolation of fault is not easy in this topology

type of network

One way to categorize the different types of computer network designs is by their scope or scale. For historical reasons, the networking industry refers to nearly every type of design as some kind of area network. Common examples of area network types are:

• LAN - Local Area Network
• WLAN - Wireless Local Area Network
• WAN - Wide Area Network
• MAN - Metropolitan Area Network
• SAN - Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network
• CAN - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network
• PAN - Personal Area Network
• DAN - Desk Area Network

LAN and WAN were the original categories of area networks, while the others have gradually emerged over many years of technology evolution.

Note that these network types are a separate concept from network topologies such as bus, ring and star.

See also - Introduction to Network Topologies

LAN - Local Area Network

A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. In TCP/IP networking, a LAN is often but not always implemented as a single IPsubnet.

In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization. They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring.

WAN - Wide Area Network

As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth.

A WAN is a geographically-dispersed collection of LANs. A network device called a routerconnects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.

A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances.

LAN, WAN and Home Networking

Residences typically employ one LAN and connect to the Internet WAN via an Internet Service Provider (ISP) using a broadband modem. The ISP provides a WAN IP address to the modem, and all of the computers on the home network use LAN (so-called private) IP addresses. All computers on the home LAN can communicate directly with each other but must go through a central gateway, typically a broadband router, to reach the ISP.

Other Types of Area Networks

While LAN and WAN are by far the most popular network types mentioned, you may also commonly see references to these others:

• Wireless Local Area Network - a LAN based on WiFi wireless network technology
• Metropolitan Area Network - a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity such as a government body or large corporation.
• Campus Area Network - a network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus.
• Storage Area Network - connects servers to data storage devices through a technology like Fibre Channel.
• System Area Network - links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network

computer crime

Computer Crime, E-Crime, Hi-Tech Crime or Electronic Crime is a crime in which a computer plays an essential part.

This type of crime is the illegal exploitation of computer technologies, usually involving the Internet, to support crimes such as fraud, identity theft, sharing of information, and embezzlement.

Exactly what is illegal varies greatly from territory to territory. Consequently, the growth of international data communications and in particular the Internet has made these crimes both more common and more difficult to police. Luckily there are people fighting computer crime and it is taken very seriously by government agencies. See below for a link to the U.S. Department of Justice's website about e-crime and their computer forensics activities.

Examples of computer crime are:

* Fraud achieved by the manipulation of computer records.
* Spamming wherever outlawed completely or where regulations controlling it are violated.
* Deliberate circumvention of computer security systems.
* Unauthorised access to or modification of
o programs (see software cracking and hacking).
o data.
* Intellectual property theft, including software piracy.
* Industrial espionage by means of access to or theft of computer materials.
* Identity theft where this is accomplished by use of fraudulent computer transactions.
* Writing or spreading computer viruses or worms.
* Salami slicing is the practice of stealing money repeatedly in extremely small quantities
* Denial-of-service attack, where company websites are flooded with service requests and their website is overloaded and either slowed or crashes completely
* Making and digitally distributing child pornography