MOTHERBOARD AND ITS COMPONENTS

MOTHERBOARD AND ITS COMPONENTS [16 Marks]

Chapter 1

Chapter Details
1.1 Introduction
MOTHERBOARD AND ITS COMPONENTS
    Chipset Architecture
North/South Bridge Architecture
1.4 Buses on Motherboard(Expansion OR I/O Slot)
Hub Architecture
ISA
EISA
PCI
PCI-X
Intel Chipset 915G
Intel Chipset 945G

1.1 INTRODUCTION

A computer is a programmable electronic device that can Store , retrieve and process data. The architecture of computer is the conceptual design and fundamental operational structure of a computer system, whereas computer maintenance is the practice of keeping computers in a good state. The basic structure of the computer is shown in fig. 1.1. Figure 1.1: Components of motherboard Based on these structures different Personal Computers (PCs) are designed. The different components and peripherals in a modern PC system are:

1. Motherboard
2. Processor
3. Memory (RAM/ROM)
4. Interface cards/daughter boards.
5. SMPS
6. Hard disk drive
7. CD-ROM drive
8. Keyboard
9. Mouse
10. Monitor

Motherboard and Its Components

The most important component in any PC is the motherboard, also called as system board. It houses a microprocessor, memory and slots for expansion, of the system. Some motherboards also contain the drive interface logic, printer interface logic and serial interface logic integrated on it. Motherboard comes in different sizes, shapes and models. The height and width of the motherboard is known as motherboard form factor.

The main functional blocks of a motherboard are as follows:
i. CPU
ii. BIOS
iii. RAM
iv. Cache memory
v. Bus expansion slots
vi. On-board IO connectors
vii. On-board IDE connectors.
i. CPU:
 The Central Processing Unit (CPU) is the brain of the computer in which
majority of the computing tasks are performed. The CPU may have a heat sink
installed on it, to dissipate heat generated by the CPU.
ii. BIOS (Basic Input Output System):
 BIOS is a ROM chip. It contains programs that
are necessary for the PC to boot and to access the various system components.
BIOS also contains the programs for POST (Power On Self Test).
iii. RAM (Random Access Memory):
 RAM is used for storing programs temporarily.
Generally RAM is located on SIMM (Single Inline Memory Module) or DIMM
(Dual Inline Memory Module).
iv. Cache Memory:
 The cache is the fastest memory which lies between CPU and
RAM. The CPU can access the frequently required data from cache more rapidly
than from RAM.
v. Bus Expansion Slots/I/O Slots:
 System expansion is possible using the bus
expansion slots in which the adapters are installed. The different types of slots such
as ISA, VESA, PCI are available on motherboard.
vi. On-board I/O Connectors:
 In recent systems one or two serial ports (com1, com2)
and parallel ports (LPT1, LPT2) are present on motherboard.
vii. On-board IDE Connectors:
 Similar to serial and parallel parts the motherboard
may have IDE connectors for connecting. Floppy Disk Drives (FDD), Hard Disk
Drives (HDD) and CD Drives.

1.2 CHIPSET BASICS

To reduce the number of chips on the motherboard, the logics around the processor are integrated into two or three chips. These chips work in conjunction with processor. These chips contain more than one logic like DMA logic, timer logic, interrupt logic and peripheral interface logic. Hence these chips are called as chipset. In PC, the chipset represents the connection between the processor and everything else. The processor can’t talk to the memory, adapter boards, devices without going through the chipset/ If processor is the brain, the chipset is spine and central nervous system of computer. The chipset manufacturers are Intel, Acer Labs, Silicon Integrated System (SIS) and AMD etc. To maximize performance of a motherboard picks up a proper microprocessor and a good chipset.

1.2.1 Chipset Architecture

Intel has used two different chipset architectures:
i. North/South bridge architecture
ii. Hub architecture.
All the chipsets introduced from the 800 series onwards, use the hub architecture.
1.2.2 North/South Bridge Architecture:
Most of Intel’s earlier chipsets are broken into a multi-tiered architecture, consisting
North and South Bridge components as well as a Super I/O Chip. Fig. 1.2 shows
North/South Bridge architecture.
1>The North Bridge:
 North bridge is the connection between the high-speed
processor bus and the slower AGP and PCI buses. Sometimes, it is referred as the
PAC (PCI/AGP Controller). It is the main component of the motherboard which is
placed beside the processor. It runs at full motherboard (processor bus) speed.
Chipset


Most of the modern chipsets use a single chip North bridge, however older ones
consist of up to three different chips.
2>The South Bridge:
                                       South bridge is the connection between the PCI bus and the
slower ISA bus. It is the lower speed component in the chipset and has always been
a single individual chip. The south bridge connects to the 33 MHz PCI bus and
contains the interface or bridge to the 8 MHz ISA bus. It also contains dual IDE
hard disk controller interfaces, one to two USB interfaces and even CMOS RAM
and real-time clock functions. It contains all the components that make up the ISA
bus, including the interrupt and DMA controllers.
3>The Super I/O Chip: 
     It is connected to the 8 MHz ISA bus and contains all the
standard peripherals that are built into a motherboard such as serial ports, parallel
ports, floppy controller, keyboard and mouse interface.
Some motherboards have a super south bridge containing south bridge and super
I/O functions into a single chip.

Figure 1.2: Architecture of north/south bridge-7

1.2.3 Hub Architecture

The newer chipsets from Intel use hub architecture. In hub architecturem, North bridge chip is called as Memory Controller Hub (MCH) and South bridge chip is called as I/O Controller Hub (ICH). Systems that include integrated graphics use a Graphics Memory Controller Hub (GMCH) instead of MCH. The standard South/North bridges are connected through PCI bus, but here they are connected via a dedicated hub interface that is at least twice as fast as PCI. This design allows a much greater throughput for PCI devices because there is no south bridge chip using the PCI bus. There are two main variations in the hub interface: i. AHA (Accelerated Hub Architecture): It is used by 8xx?series of chipsets. It has twice the throughput of PCI. ii. DMI (Direct Media Interface): It is used by 9xxand 3x series chipsets. DMI is basically a dedicated 4 bit wide PCI Express connection allowing 1 GBps in each direction. Following fig. 1.3 shows hub architecture: Figure 1.3: Hub architecture / architecture of Intel Chipset 915 G

1.3 ARCHITECTURE OF INTEL CHIPSETS

As Intel develops new processor, it develops chipsets and motherboards simultaneously. Here we are going to study architecture of Intel chipset 915 G and 945 G.

1.3.1 Intel Chipset 915 G

The Intel 915 chipset family was introduced in 2004. This family has six members - 910 GL, 915 PL, 915 P, 915 G, 915 GV and 915 GL, all of which support the 90 mm Pentium-4 prescott core. These chipsets are the first to support the socket 775 processor interface. This chipset model support the Hyper Threading (HT) Technology feature built into most recent Pentium 4 processors. It supports bus speed upto 800 MHz. It supports dual channel DDR memory upto 400 MHz and PCI - Express X1 and PCI version 2.2 expansion slots. This also supports the new DDR2 memory standard at speed upto 533 MHz. The 915 G has a PCI express X16 slot as well as integrated Intel Graphics Media Accelerator 900. All 915 series MCH/GMCH chips use the new ICH6 family of South Bridge replacements.

Features of Intel 915 G Chipset (refer fig. 1.3)
1. Code Name              : Grandsdale - G
2. Port Number            : 828915 G
3. Bus Speeds             : 800 / 533 MHz
4. Supported Processor    : Pentium IV, Celeron, Celeron-D
5. SMP (dual CPUs)        : No
6. Memory Types           : DDR 333 / 400, Dual Channel DDR2
7. Maximum Memory         : 4GB
8. Memory banks           : 2
9. PCI Support            : PCI Expres-X1, X16, PCI 2.2
10. PCI Speed/Width       : 33MHz/32 bit
11. PCI Express X-16 Video: Yes
12. AGP slot              : No
13. Integrated Video      : Extreme Graphics 3
14.South Bridge (Hub): ICH6 family-9

1.3.2 Intel Chipset 945 G

The Intel 945 Express Chipset family was released in 2005. It includes 3 members 945 G, 945 P and 945 PL. This chipset is the first to support Intel’s new dual core Pentium D processors. It also supports Pentium-4 Hyper Threading (HT) Technology processors using socket 775. The 945 G is aimed as the ‘Performance PC’. It offers Front Side Bus (FSB) speed up to 1,066 MHz. It supports up to 4GB of dual-channel DDR2 memory (2 pairs) running at upto 667 MHz. It features PCI Express X16 support and also incorporates Intel Graphics Media Accelerator 950 integrated graphics. All members of the 945 family support the ICH7 family of I/O controller hub chips. The ICH7 family differs from ICH6 in the following ways: i. It has support for 300 MBps serial ATA. ii. It has support for SATA RAID 5 and Matrix RAID. iii. It has support for two additional PCI-Express X1 ports.

Features of Intel 945 G Chipset
1. Code Name              : Lakeport GG
2. Port Number            : 82945 G
3. Bus Speed              : 1066 / 800 / 533 MHz
4. Supported Processors   : Pentium-D, Pentium-4 with HT Technology
5. SMP (Dual CPUs)        : No
6. Memory Types           : DDR2 667/533/400 MHz dual channel DDR2
7. Maximum Memory         : 4GB
8. Memory banks           : 2
9. PCI Support            : PCI Expres-X1, X16, PCI 2.3
10. PCI Speed/Width       : 33MHz/32 bit
11. PCI Express X-16 Video: Yes
12. AGP slot              : No
13. Integrated Video      : GMA 900
14. South Bridge (Hub)    : ICH7 family

Figure 1.4: Architecture of Intel Chipset 945 G

1.4 BUSES ON MOTHERBOARD(EXPANSION OR I/O SLOT)

The heart of any motherboard is the various buses that carry signals between the components. Bus is a group of wires through which the CPU communicates with memory, coprocessor, keyboard and other ICs in the motherboard. The PC has a hierarchy of different buses as the processor bus and I/O buses. The processor bus is also called as Front Side Bus (FSB). It is the communication pathway between the CPU and motherboard chipset. This bus runs at the full motherboard speed. 1-11 The I/O bus enables your CPU to communicate with peripheral devices. It enables you to add devices to your computer to expand its capabilities.

The different I/O buses on motherboard are as follows:
i. ISA                        ii. PCI-X
iii. PCI-Xpress               iv. PCMCIA
v. AGP                        vi. Processor Bus (FSB)

1.4.1 ISA (Industry Standard Architecture)

ISA is the 8 bit bus architecture that was used in IBM-PC in 1981. It was later expanded to 16 bits. It is a very slow speed bus which is ideal for certain slow speed or older peripherals such as plug-in modems, sound cards etc.

Features of 8 bit ISA Bus
i. It provides 8 data lines.
ii. It has four DMA channels.
iii. It has eight IRQ levels.
iv. 20 addressing lines.
v. 8 bit ISA slot handles 1 MB of memory.
vi. 8 bit version ran at 4.77 MHz
vii. It provides Bandwidth 4.17 MBps.
Features of 16 bits ISA Bus
It was introduced as 16 bit ISA bus used in IBM PC/AT in 1984.
i. It has 16 data lines.
ii. 24 address lines
iii. 8-DMA channels
iv. Interrupt requests
v. Backward compatible with 8 bit TSA bus.
vi. Ran at 8.33 MHz.
vii. Bandwidth 8.33 MBps

1.4.2 EISA (Extended ISA)

This architecture support 32 bit buses with much higher data transfer rates upto 33 MBps. It provides backward compatibility to 8 bit and 16 bit ISA cards. 1-

Features
i. 32 bit data bus
ii. It handles 4GB of memory.
iii. 8.33 MHz clock speed
iv. Bandwidth 33 MBps
v. Backward compatible with 8 bit and 16 bit ISA cards.
vi. Support 64 kB T10 addresses.

1.4.3 PCI (Peripheral Component Interconnect) : PCI is the acronym for Peripheral Component Interconnect. It is a high speed bus that connects high performance peripherals like video adapters, drive adapters and network adapters to the chipset, processor and memory. PCI bypasses the standard I10 bus. IT uses the system bus to increase the bus clock speed and take full advantage of the CPUs data path. The most recent motherboards usually provide 4 or 5 PCI slots. The 1 PCT bus can be either 32 bits or 64 bits wide. Information is transferred across the bus at 33 MHz and 32 bits at a time. The Bandwidth is 133 MBps. PCI with 64 bits of 66.66 MHz provides bandwidth 533 MBps. These variations are used only on server or workstation types boards.

>1.4.4 PCI-X (Peripheral Component Interconnect Extended)

It is standard designed computer bus or expansion slot advanced to PCI. PCI-X is faster version of PCI running at twice the speed of PCI. PCI-X was developed by IBM, HP and Compaq. PCI X doubles the clock speed from 66 MHz to 133 MHz and hence amount of data exchanged between the computer processor and peripherals. Standard PCI supports up to 64 bit at 66 MHz.

THANKS FOR YOUR VISITING

CRT VS LCD (CAM)

There are important differences to consider between cathode ray tube (CRT) and liquid crystal display (LCD) monitors. Some advantages of CRT monitors include:

• CRT monitors are less expensive than LCDs, though LCD prices continue to fall.
• CRT monitors typically produce more accurate colors, though LCDs are improving.
• CRT monitors don't usually exhibit the blurring and ghosting that LCDs do, because they can redraw the screen faster.
• CRT monitors support multiple resolutions without a decrease in picture quality.
• CRT monitors are sturdier and more difficult to damage.

MAJOR ADVANTAGES OF CRT (Pros of CRT, Cons of LCD)

POINTS	CRT	LCD
Dead / Stuck Pixel	There is no such problem in CRTs as images are painted on the screen.	LCD panels are prone to dead or stuck pixels (or dots) on the screen due to their manufacturing process. However, stiff competition has made many manufacturers adopt zero dead pixel / stuck pixel warranties for their products.
Response Time	CRTs already have a very fast response time hence this attribute does not apply to it.	This attribute is specially for LCDs as the lower the response rate is, the better the chance of avoiding "ghosting" effect.
Price	Affordable and cheaper than LCDs due to their declining popularity. 17 inch CRT costs around $160 19 inch CRT costs around $225	Considerably more expensive, but prices are dropping fast. 17 inch LCD costs around $275 19 inch LCD costs around $330
Native Resolution	Can be used at any resolution up to the maximum supported. No image quality is lost at any resolution.	Must be used at its native resolution (maximum resolution) for best quality. Using the display at a lower resolution will result interpolation (scaling of the image), causing image quality loss. This is one of the major reasons for CRTs being in use by gamers as the high native resolution that LCD demands may not deliver smooth frame rates.
Max Colors	32 bit	8-Bit max, 16.7 million colors.
Viewing Angle	Wide viewing angle	Narrow viewing angle, depending on technology employed.
Video	Ideal for any video including HD	Not ideal for Standard Definition videos, but great for High Definition videos
Blackness	True Black	Between Dark Gray to Gray

THANKING YOU FOR YOUR VISITING

PLEASE WRITE YOUR QUERY IN COMMENT

PRADEEP

COMPUTER VIRUS (CAM)

DEFINITION:-

A computer virus is a type of malware that, when executed, replicates by inserting copies of itself (possibly modified) into other computer programs, data files, or the boot sector of the hard drive; when this replication succeeds, the affected areas are then said to be "infected".  Viruses often perform some type of harmful activity on infected hosts, such as stealing hard disk space or CPU time, accessing private information, corrupting data, displaying political or humorous messages on the user's screen, spamming their contacts, or logging their keystrokes. However, not all viruses carry a destructive payload or attempt to hide themselves—the defining characteristic of viruses is that they are self-replicating computer programs which install themselves without the user's consent.

Or

A computer virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes. Viruses can also replicate themselves. All computer viruses are man-made. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt. An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing security systems.

SYMPTOM OF VIRUS:-

1. Hardware Troubles – It’s Alive!

If sudden sounds of the CD-ROM tray opening completely out if its own will give you the heebiejeebies, I don’t blame you! If your hardware – computer, printer, etc. – started acting up on its own, without you requesting any action by means of keyboard or mouse, you are likely having a virus in your computer system. When you work on the computer, especially if you are performing some actions by using programs,your hard drive is expected to be making some noises.

If you are not doing anything, and your computer seems to be putting in extra effort and looks like it is communicating with 8th dimension completely by itself, consider an emergency antivirus scan.

2. No Response – Is Anyone Home?

We’ve all been there: working away, and then BAM – nothing happens! You can’t move your mouse, the keyboard does zilch, you go into panic mode “ouch, did I save that document I was writing for the past 2 hours?”…. (Now, in the voice of “desperate housewives narrator: “Yes. We all had the frozen iceberg for a computer before”). Lockup alone may not necessarily mean you have a virus – it could also be a symptom of a desperate need for a cleanup (we will be going over it in another article) – but if it presents itself in array of other symptoms, be on a lookout for a virus.

3. Slow Performance – Are We There yet?

If you notice that certain actions take much longer then usual, you should be concerned. As in the previous paragraphs – you must account for specifics of certain files and programs when making a judgment of the slow performance: one PDF document may take much longer time to open simply because it is of a much larger size, and it will not be indicative of the computer virus. However, keep in mind that some viruses can reproduce and multiply your files and overcrowd disk space, overloading disk usage. In another example, when you are browsing your documents folders and you notice that it takes – unusually – longer to browse from one folder to another, or if it takes more and more time to open the same program, you should be on a lookout for other computer virus symptoms.

4. Slow Startup – Easy doesn’t.

Another important symptom of a computer virus is a slow startup. Do not confuse it with wishful thinking. As a collective, we are impatient beings. Did you ever catch yourself pushing an elevator button, mumbling to yourself, “It must be the slowest elevator ever”? My point exactly! When considering the startup process – think of the typical (however slow you may feel it is) to the actual startup time. Does it seem to be much slower then usual? Does it seem to just sit there, and not even a blink or a squeak happens?

If it takes way too long, then it may be a symptom of a viral infection in your computer.

5. Crashing – Crash and Burn, Baby!

When your computer crashes spontaneously, be careful. After computer restarts, you may notice it does not seem to run normally. If it self-restarts frequently, every few minutes – beware of a virus. This symptom alone may indicate that your system is infected. If your computer crashed, best course of action – Do Not Resuscitate and call your IT support company.

6. Missing files – Gone With the Wind…

When you notice that applications on your computer do not work correctly, you may also notice some of your files are missing. That includes different types of files. Some may be the files that you created, such as images or documents you had saved on your drive. You may physically notice absence of those when you actually look for them and can’t seem to find them anywhere. As a result of computer virus infection your computer may also be missing system files. As a user, you may not know what they are and may not notice they are gone, however, if you are trying to use certain applications (browser, email client, document editor, etc.) sometimes those application will refuse to run properly and pop up a warning for you that “critical file is missing” – usually accompanied by the name of the file that is MIA – alerting you to a loss of some files.

7. Disks or Disk Drives Are Not Accessible – Who Ate My Porridge?

If you are loosing the network connection – or worse yet cannot connect to the USB drive you just plugged in, or you go to My Computer and only see one drive instead of your usual X number of drives, you may be in trouble. If you cannot connect to all, some of the drives or cannot access your CD-ROM, it may be one of the symptoms indicating your computer is infected.

8. Extra Files – Who Sat In My Chair?

You may visually notice extra pop ups and extra programs that seem to be running on your computer, especially on startup. You may notice (if you check for it) that your disk space suddenly quadrupled in size without you making 200 copies of your vacation photos folder on your C: drive.

9. Printer Issues – Is This Thing On?

If you cannot get your documents to print correctly, or cannot print at all, you may be dealing with a virus. First, rule out your printer not being turned on. Next, ensure it is connected to your network and is not offline. If it turned on and it is online (connected to your network), and you still have problems with printer, your computer system may have a virus and may affect not just your drive, but you network, as well.

10. Unusual Error Messages – Did You See That?

This may include gibberish messages, messages you hadn’t seem before, undesired ad messages and such. Special attention must be paid to messages that disguise themselves as anti-virus warning messages. They are designed to trick you into thinking that you are at risk, and must take action to protect your computer system. Sometimes that is how the virus introduces itself into the system, and sometimes it may already be in your system, and that is how it takes over it, making your more and more vulnerable, and doing further damage to your computer. Again, when you are in doubt, it is best to call professional computer support company.

PROTECTION FROM VIRUS-

1: Install quality antivirus

Many computer users believe free antivirus applications, such as those included with an Internet service provider's bundled service offering, are sufficient to protect a computer from virus or spyware infection. However, such free anti-malware programs typically don't provide adequate protection from the ever-growing list of threats.
Instead, all Windows users should install professional, business-grade antivirus software on their PCs. Pro-grade antivirus programs update more frequently throughout the day (thereby providing timely protection against fast-emerging vulnerabilities), protect against a wider range of threats (such as rootkits), and enable additional protective features (such as custom scans).

2: Install real-time anti-spyware protection

Many computer users mistakenly believe that a single antivirus program with integrated spyware protection provides sufficient safeguards from adware and spyware. Others think free anti-spyware applications, combined with an antivirus utility, deliver capable protection from the skyrocketing number of spyware threats.
Unfortunately, that's just not the case. Most free anti-spyware programs do not provide real-time, or active, protection from adware, Trojan, and other spyware infections. While many free programs can detect spyware threats once they've infected a system, typically professional (or fully paid and licensed) anti-spyware programs are required to prevent infections and fully remove those infections already present.

3: Keep anti-malware applications current

Antivirus and anti-spyware programs require regular signature and database updates. Without these critical updates, anti-malware programs are unable to protect PCs from the latest threats.
In early 2009, antivirus provider AVG released statistics revealing that a lot of serious computer threats are secretive and fast-moving. Many of these infections are short-lived, but they're estimated to infect as many as 100,000 to 300,000 new Web sites a day.
Computer users must keep their antivirus and anti-spyware applications up to date. All Windows users must take measures to prevent license expiration, thereby ensuring that their anti-malware programs stay current and continue providing protection against the most recent threats. Those threats now spread with alarming speed, thanks to the popularity of such social media sites as Twitter, Facebook, and My Space.

4: Perform daily scans

Occasionally, virus and spyware threats escape a system's active protective engines and infect a system. The sheer number and volume of potential and new threats make it inevitable that particularly inventive infections will outsmart security software. In other cases, users may inadvertently instruct anti-malware software to allow a virus or spyware program to run.
Regardless of the infection source, enabling complete, daily scans of a system's entire hard drive adds another layer of protection. These daily scans can be invaluable in detecting, isolating, and removing infections that initially escape security software's attention.

5: Disable autorun

Many viruses work by attaching themselves to a drive and automatically installing themselves on any other media connected to the system. As a result, connecting any network drives, external hard disks, or even thumb drives to a system can result in the automatic propagation of such threats.
Computer users can disable the Windows autorun feature by following Microsoft's recommendations, which differ by operating system. Microsoft Knowledge Base articles 967715 and 967940 are frequently referenced for this purpose.

6: Disable image previews in Outlook

Simply receiving an infected Outlook e-mail message, one in which graphics code is used to enable the virus' execution, can result in a virus infection. Prevent against automatic infection by disabling image previews in Outlook.
By default, newer versions of Microsoft Outlook do not automatically display images. But if you or another user has changed the default security settings, you can switch them back (using Outlook 2007) by going to Tools | Trust Center, highlighting the Automatic Download option, and selecting Don't Download Pictures Automatically In HTML E-Mail Messages Or RSS.

7: Don't click on email links or attachments

It's a mantra most every Windows user has heard repeatedly: Don't click on email links or attachments. Yet users frequently fail to heed the warning.
Whether distracted, trustful of friends or colleagues they know, or simply fooled by a crafty email message, many users forget to be wary of links and attachments included within email messages, regardless of the source. Simply clicking on an email link or attachment can, within minutes, corrupt Windows, infect other machines, and destroy critical data.
Users should never click on email attachments without at least first scanning them for viruses using a business-class anti-malware application. As for clicking on links, users should access Web sites by opening a browser and manually navigating to the sites in question.

8: Surf smart

Many business-class anti-malware applications include browser plug-ins that help protect against drive-by infections, phishing attacks (in which pages purport to serve one function when in fact they try to steal personal, financial, or other sensitive information), and similar exploits. Still others provide "link protection," in which Web links are checked against databases of known-bad pages.
Whenever possible, these preventive features should be deployed and enabled. Unless the plug-ins interfere with normal Web browsing, users should leave them enabled. The same is true for automatic pop-up blockers, such as are included in Internet Explorer 8, Google's toolbar, and other popular browser toolbars.
Regardless, users should never enter user account, personal, financial, or other sensitive information on any Web page at which they haven't manually arrived. They should instead open a Web browser, enter the address of the page they need to reach, and enter their information that way, instead of clicking on a hyperlink and assuming the link has directed them to the proper URL. Hyperlinks contained within an e-mail message often redirect users to fraudulent, fake, or unauthorized Web sites. By entering Web addresses manually, users can help ensure that they arrive at the actual page they intend.
But even manual entry isn't foolproof. Hence the justification for step 10: Deploy DNS protection. More on that in a moment.

9: Use a hardware-based firewall

Technology professionals and others argue the benefits of software- versus hardware-based firewalls. Often, users encounter trouble trying to share printers, access network resources, and perform other tasks when deploying third-party software-based firewalls. As a result, I've seen many cases where firewalls have simply been disabled altogether.
But a reliable firewall is indispensable, as it protects computers from a wide variety of exploits, malicious network traffic, viruses, worms, and other vulnerabilities. Unfortunately, by itself, the software-based firewall included with Windows isn't sufficient to protect systems from the myriad robotic attacks affecting all Internet-connected systems. For this reason, all PCs connected to the Internet should be secured behind a capable hardware-based firewall.

10: Deploy DNS protection

Internet access introduces a wide variety of security risks. Among the most disconcerting may be drive-by infections, in which users only need to visit a compromised Web page to infect their own PCs (and potentially begin infecting those of customers, colleagues, and other staff).
Another worry is Web sites that distribute infected programs, applications, and Trojan files. Still another threat exists in the form of poisoned DNS attacks, whereby a compromised DNS server directs you to an unauthorized Web server. These compromised DNS servers are typically your ISP's systems, which usually translate friendly URLs such as yahoo.com to numeric IP addresses like 69.147.114.224.

TRANSMISSION MEDIA(CN)

TRANSMISSION MEDIA:

The means through which data is transformed from one place to another is called transmission or communication media. There are two categories of transmission media used in computer communications.

• BOUNDED/GUIDED MEDIA
• UNBOUNDED/UNGUIDED MEDIA

1. BOUNDED MEDIA:
Bounded media are the physical links through which signals are confined to narrow path. These are also called guide media. Bounded media are made up oa external conductor (Usually Copper) bounded by jacket material. Bounded media are great for LABS because they offer high speed, good security and low cast. However, some time they cannot be used due distance communication. Three common types of bounded media are used of the data transmission. These are

• Coaxial Cable
• Twisted Pairs Cable
• Fiber Optics Cable

COAXIAL CABLE:
Coaxial cable is very common & widely used commutation media. For example TV wire is usually coaxial.
Coaxial cable gets its name because it contains two conductors that are parallel to each other. The center conductor in the cable is usually copper. The copper can be either a solid wire or stranded martial.
Outside this central Conductor is a non-conductive material. It is usually white, plastic material used to separate the inner Conductor form the outer Conductor. The other Conductor is a fine mesh made from Copper. It is used to help shield the cable form EMI.
Outside the copper mesh is the final protective cover. (as shown in Fig)
The actual data travels through the center conductor in the cable. EMI interference is caught by outer copper mesh. There are different types of coaxial cable vary by gauge & impedance.
Gauge is the measure of the cable thickness. It is measured by the Radio grade measurement, or RG number. The high the RG number, the thinner the central conductor core, the lower the number the thicker the core.
Here the most common coaxial standards.

• 50-Ohm RG-7 or RG-11 : used with thick Ethernet.
• 50-Ohm RG-58 : used with thin Ethernet
• 75-Ohm RG-59 : used with cable television
• 93-Ohm RG-62 : used with ARCNET.

CHARACTERISTICS OF COAXIAL CABLE:

• Low cost
• Easy to install
• Up to 10Mbps capacity
• Medium immunity form EMI
• Medium of attenuation

ADVANTAGESOF  COAXIAL CABLE

• Inexpensive
• Easy to wire
• Easy to expand
• Moderate level of EMI immunity
• DISADVANTAGE OF COAXIAL CABLE---
• Single cable failure can take down an entire network

Twisted Pair Cable

The most popular network cabling is Twisted pair. It is light weight, easy to install, inexpensive and support many different types of network. It also supports the speed of 100 mps.Twisted pair cabling is made of pairs of solid or stranded copper twisted along each other. The twists are done to reduce vulnerably to EMI and cross talk. The number of pairs in the cable depends on the type. The copper core is usually 22-AWG or 24-AWG, as measured on the American wire gauge standard. There are two types of twisted pairs cabling
1. Unshielded twisted pair (UTP)
2. Shielded twisted pair (STP)

1. Unshielded twisted pair (UTP)
UTP is more common. It can be either voice grade or data grade depending on the condition. UTP cable normally has an impedance of 100 ohm. UTP cost less than STP and easily available due to its many use. There are five levels of data cabling
Category 1
These are used in telephone lines and low speed data cable.
Category 2
These cables can support up to 4 mps implementation.
Category 3
These cable supports up to 16 mps and are mostly used in 10 mps.
Category 4
These are used for large distance and high speed. It can support 20mps.
Category 5
This is the highest rating for UTP cable and can support up to 100mps.
UTP cables consist of 2 or 4 pairs of twisted cable. Cable with 2 pair use RJ-11 connector and 4 pair cable use RJ-45 connector.
Characteristics of UTP

• low cost
• easy to install
• High speed capacity
• High attenuation
• Effective to EMI
• 100 meter limit

Advantages of UTP

• Easy installation
• Capable of high speed for LAN
• Low cost

Disadvantages of UTP

• Short distance due to attenuation

2.Shielded twisted pair (STP)
It is similar to UTP but has a mesh shielding that's protects it from EMI which allows for higher transmission rate.
IBM has defined category for STP cable.
Type 1
STP features two pairs of 22-AWG
Type 2
This type include type 1 with 4 telephone pairs
Type 6
This type feature two pairs of standard shielded 26-AWG
Type 7
This type of STP consist of 1 pair of standard shielded 26-AWG
Type 9
This type consist of shielded 26-AWG wire
Characteristics of STP--

• Medium cost
• Easy to install
• Higher capacity than UTP
• Higher attenuation, but same as UTP
• Medium immunity from EMI
• 100 meter limit

Advantages of STP:

• Shielded
• Faster than UTP and coaxial

Disadvantages of STP:

• More expensive than UTP and coaxial
• More difficult installation
• High attenuation rate

Fiber Optics

Fiber optic cable uses electrical signals to transmit data. It uses light. In fiber optic cable light only moves in one direction for two way communication to take place a second connection must be made between the two devices. It is actually two stands of cable. Each stand is responsible for one direction of communication. A laser at one device sends pulse of light through this cable to other device. These pulses translated into "1's" and "0's" at the other end.
In the center of fiber cable is a glass stand or core. The light from the laser moves through this glass to the other device around the internal core is a reflective material known asCLADDING. No light escapes the glass core because of this reflective cladding.
Fiber optic cable has bandwidth more than 2 gbps (Gigabytes per Second)
Characteristics Of Fiber Optic Cable:

• Expensive
• Very hard to install
• Capable of extremely high speed
• Extremely low attenuation
• No EMI interference

Advantages Of Fiber Optic Cable:

• Fast
• Low attenuation
• No EMI interference

Disadvantages Fiber Optics:

• Very costly
• Hard to install
•  

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COMPUTER NETWORK

Network topology

Network topology is the arrangement of the various elements (links, nodes, etc.) of a computer network. Essentially, it is the topological structure of a network, and may be depicted physically or logically. Physical topology refers to the placement of the network's various components, including device location and cable installation, while logical topology shows how data flows within a network, regardless of its physical design. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ between two networks, yet their topologies may be identical.

A good example is a local area network (LAN): Any given node in the LAN has one or more physical links to other devices in the network; graphically mapping these links results in a geometric shape that can be used to describe the physical topology of the network. Conversely, mapping the data flow between the components determines the logical topology of the network.

Topology

There are two basic categories of network topologies:

1. Physical topologies
2. Logical topologies

The shape of the cabling layout used to link devices is called the physical topology of the network. This refers to the layout of cabling, the locations of nodes, and the interconnections between the nodes and the cabling. The physical topology of a network is determined by the capabilities of the network access devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunications circuits.

The logical topology in contrast, is the way that the signals act on the network media, or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices. A network's logical topology is not necessarily the same as its physical topology. For example, the original twisted pair Ethernet using repeater hubs was a logical bus topology with a physical star topology layout. Token Ring is a logical ring topology, but is wired a physical star from the Media Access Unit.

The logical classification of network topologies generally follows the same classifications as those in the physical classifications of network topologies but describes the path that the data takes between nodes being used as opposed to the actual physical connections between nodes. The logical topologies are generally determined by network protocols as opposed to being determined by the physical layout of cables, wires, and network devices or by the flow of the electrical signals, although in many cases the paths that the electrical signals take between nodes may closely match the logical flow of data, hence the convention of using the terms logical topology and signal topology interchangeably.

Logical topologies are often closely associated with Media Access Control methods and protocols. Logical topologies are able to be dynamically reconfigured by special types of equipment such as routers and switches.

Diagram of different network topologies.

The study of network topology recognizes eight basic topologies:

• Point-to-point
• Bus
• Star
• Ring or circular
• Mesh
• Tree
• Hybrid
• Daisy chain

Point-to-point

The simplest topology is a permanent link between two endpoints. Switched point-to-point topologies are the basic model of conventional telephony. The value of a permanent point-to-point network is unimpeded communications between the two endpoints. The value of an on-demand point-to-point connection is proportional to the number of potential pairs of subscribers, and has been expressed as Metcalfe's Law.

Permanent (dedicated)

Easiest to understand, of the variations of point-to-point topology, is a point-to-point communications channel that appears, to the user, to be permanently associated with the two endpoints. A children's tin can telephone is one example of a physical dedicated channel.

Within many switched telecommunications systems, it is possible to establish a permanent circuit. One example might be a telephone in the lobby of a public building, which is programmed to ring only the number of a telephone dispatcher. "Nailing down" a switched connection saves the cost of running a physical circuit between the two points. The resources in such a connection can be released when no longer needed, for example, a television circuit from a parade route back to the studio.

Switched:

Using circuit-switching or packet-switching technologies, a point-to-point circuit can be set up dynamically, and dropped when no longer needed. This is the basic mode of conventional telephony.

Bus Topology

Bus network topology

In local area networks where bus topology is used, each node is connected to a single cable. Each computer or server is connected to the single bus cable. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted. Since the bus topology consists of only one wire, it is rather inexpensive to implement when compared to other topologies. However, the low cost of implementing the technology is offset by the high cost of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If the network cable is terminated on both ends and when without termination data transfer stop and when cable breaks, the entire network will be down.

Linear bus

The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has exactly two endpoints (this is the 'bus', which is also commonly referred to as the backbone, or trunk) – all data that is transmitted between nodes in the network is transmitted over this common transmission medium and is able to be received by all nodes in the network simultaneously.^[1]

Note: When the electrical signal reaches the end of the bus, the signal "echoes" back down the line, causing unwanted interference. As a solution, the two endpoints of the bus are normally terminated with a device called a terminator that prevents this echo.

Distributed bus

The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has more than two endpoints that are created by adding branches to the main section of the transmission medium – the physical distributed bus topology functions in exactly the same fashion as the physical linear bus topology (i.e., all nodes share a common transmission medium).

Star Topology

Star network topology

In local area networks with a star topology, each network host is connected to a central hub with a point-to-point connection. In Star topology every node (computer workstation or any other peripheral) is connected to central node called hub or switch. The switch is the server and the peripherals are the clients. The network does not necessarily have to resemble a star to be classified as a star network, but all of the nodes on the network must be connected to one central device. All traffic that traverses the network passes through the central hub. The hub acts as a signal repeater. The star topology is considered the easiest topology to design and implement. An advantage of the star topology is the simplicity of adding additional nodes. The primary disadvantage of the star topology is that the hub represents a single point of failure.

Extended star

A type of network topology in which a network that is based upon the physical star topology has one or more repeaters between the central node (the 'hub' of the star) and the peripheral or 'spoke' nodes, the repeaters being used to extend the maximum transmission distance of the point-to-point links between the central node and the peripheral nodes beyond that which is supported by the transmitter power of the central node or beyond that which is supported by the standard upon which the physical layer of the physical star network is based.

If the repeaters in a network that is based upon the physical extended star topology are replaced with hubs or switches, then a hybrid network topology is created that is referred to as a physical hierarchical star topology, although some texts make no distinction between the two topologies.

Distributed Star

A type of network topology that is composed of individual networks that are based upon the physical star topology connected in a linear fashion – i.e., 'daisy-chained' – with no central or top level connection point (e.g., two or more 'stacked' hubs, along with their associated star connected nodes or 'spokes').

Ring Topology

Ring network topology

A network topology that is set up in a circular fashion in which data travels around the ring in one direction and each device on the ring acts as a repeater to keep the signal strong as it travels. Each device incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The network is dependent on the ability of the signal to travel around the ring. When a device sends data, it must travel through each device on the ring until it reaches its destination. Every node is a critical link.

Mesh Topology

Main article: Mesh networking

The value of fully meshed networks is proportional to the exponent of the number of subscribers, assuming that communicating groups of any two endpoints, up to and including all the endpoints, is approximated by Reed's Law.

Fully connected network

Fully connected mesh topology

A fully connected network is a communication network in which each of the nodes is connected to each other. In graph theory it known as a complete graph. A fully connected network doesn't need to use switching nor broadcasting. However, its major disadvantage is that the number of connections grows quadratic ally with the number of nodes, per the formula

and so it is extremely impractical for large networks. A two-node network is technically a fully connected network.

Partially connected

Partially connected mesh topology

The type of network topology in which some of the nodes of the network are connected to more than one other node in the network with a point-to-point link – this makes it possible to take advantage of some of the redundancy that is provided by a physical fully connected mesh topology without the expense and complexity required for a connection between every node in the network.

Tree Topology

Tree network topology

This section may be confusing or unclear to readers. (June 2011)

This particular type of network topology is based on a hierarchy of nodes. The highest level of any tree network consists of a single, 'root' node, this node connected either a single (or, more commonly, multiple) node(s) in the level below by (a) point-to-point link(s). These lower level nodes are also connected to a single or multiple nodes in the next level down. Tree networks are not constrained to any number of levels, but as tree networks are a variant of the bus network topology, they are prone to crippling network failures should a connection in a higher level of nodes fail/suffer damage. Each node in the network has a specific, fixed number of nodes connected to it at the next lower level in the hierarchy, this number referred to as the 'branching factor' of the tree. This tree has individual peripheral nodes.

1.      A network that is based upon the physical hierarchical topology must have at least three levels in the hierarchy of the tree, since a network with a central 'root' node and only one hierarchical level below it would exhibit the physical topology of a star.

2.      A network that is based upon the physical hierarchical topology and with a branching factor of 1 would be classified as a physical linear topology.

3.      The branching factor, f, is independent of the total number of nodes in the network and, therefore, if the nodes in the network require ports for connection to other nodes the total number of ports per node may be kept low even though the total number of nodes is large – this makes the effect of the cost of adding ports to each node totally dependent upon the branching factor and may therefore be kept as low as required without any effect upon the total number of nodes that are possible.

4.      The total number of point-to-point links in a network that is based upon the physical hierarchical topology will be one less than the total number of nodes in the network.

5.      If the nodes in a network that is based upon the physical hierarchical topology are required to perform any processing upon the data that is transmitted between nodes in the network, the nodes that are at higher levels in the hierarchy will be required to perform more processing operations on behalf of other nodes than the nodes that are lower in the hierarchy. Such a type of network topology is very useful and highly recommended.

Advantages

• It is scalable. Secondary nodes allow more devices to be connected to a central node.
• Point to point connection of devices.
• Having different levels of the network makes it more manageable hence easier fault identification and isolation.

Disadvantages

• Maintenance of the network may be an issue when the network spans a great area.
• Since it is a variation of bus topology, if the backbone fails, the entire network is crippled.

definition: Tree topology is a combination of Bus and Star topology.

An example of this network could be cable TV technology. Other examples are in dynamic tree based wireless networks for military, mining and otherwise mobile applications. The Naval Postgraduate School, Monterey CA, demonstrated such tree based wireless networks for border security. In a pilot system, aerial cameras kept aloft by balloons relayed real time high resolution video to ground personnel via a dynamic self healing tree based network.

Hybrid

Hybrid networks use a combination of any two or more topologies in such a way that the resulting network does not exhibit one of the standard topologies (e.g., bus, star, ring, etc.). For example a tree network connected to a tree network is still a tree network topology. A hybrid topology is always produced when two different basic network topologies are connected. Two common examples for Hybrid network are: star ring network and star bus network

• A Star ring network consists of two or more star topologies connected using a multistation access unit (MAU) as a centralized hub.
• A Star Bus network consists of two or more star topologies connected using a bus trunk (the bus trunk serves as the network's backbone).

While grid and torus networks have found popularity in high-performance computing applications, some systems have used genetic algorithms to design custom networks that have the fewest possible hops in between different nodes. Some of the resulting layouts are nearly incomprehensible, although they function quite well.

A Snowflake topology is really a "Star of Stars" network, so it exhibits characteristics of a hybrid network topology but is not composed of two different basic network topologies being connected.

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