Learn Easy Networking (MCSE)

Rajesh Yadav BJP

2011-07-22T03:20:00.001-04:00

Networking Essentials Notes - Section 2

2009-07-04T18:21:00.003-04:00

How a Network Functions

The OSI Model

International Standards Organization (ISO) specifications for network architecture.
Each layer communicates logically with its associated layer on the other computer.
Packets are sent from one layer to another in the order of the layers, from top to bottom on the sending computer and then in reverse order on the receiving computer.
Called the Open Systems Interconnect or OSI model.
Seven layered model, higher layers have more complex tasks.
Each layer provides services for the next higher layer.

OSI Layers

Application
Presentation
Session
Transport
Network
Data Link
Physical

Application Layer

Handles general network access, flow control and error recovery.
Serves as a window for applications to access network services.

Presentation Layer

Determines the format used to exchange data among the networked computers.
Responsible for protocol conversion, data translation, data encryption, data compression, character conversion, and graphics expansion.
Translates data from a format from the Application layer into an intermediate format.
Redirector operates at this level.

Session Layer

Performs name recognition and security.
Allows two applications running on different computers to establish use and end a connection called a Session.
Provides synchronization by placing checkpoints in the data stream.
Implements dialog control between communicating processes.

Transport Layer

Responsible for packet creation.
Unpacks, reassembles and sends receipt of messages at the receiving end.
Provides flow control, error handling, and solves transmission problems.
Provides an additional connection level beneath the Session layer.
Ensures that packets are delivered error free, in sequence with no losses or duplications.

Network Layer

Determines the route from the source to the destination computer.
Responsible for addressing messages and translating logical addresses and names into physical addresses.
Manages traffic such as packet switching, routing and controlling the congestion of data.

Data Link Layer

Sends data frames from the Network layer to the Physical layer.
Responsible for providing error free transmission of frames through the Physical layer.
Packages raw bits into frames for the Network layer at the receiving end.

Physical Layer

Transmits the unstructured raw bit stream over a physical medium.
Defines data encoding and bit synchronization.
Relates the electrical, optical mechanical and functional interfaces to the cable.
Defines how the cable is attached to the network adapter card.

The 802 Project Model

WAN components.
Network Adapter Cards.
Components used to create twisted-pair and coaxial cable networks.
Defines Standards for the Data Link and Physical Layers.
A crazy mnemonic for this table, but it works :-)

I Like Changing Boxers Rarely. My Butt Feels Very Sexy With Denim

802.1	Internet working
802.2	Division of Data Link Layer into sub layers LLC (Logical Link Control) Media Access Control (MAC)
802.3	CSMA/CD - Ethernet
802.4	Token Bus LAN (ARC net)
802.5	Token Ring LAN
802.6	MAN (Metropolitan Area Network)
802.7	Broadband Technical Advisory Group
802.8	Fiber-Optic Technical Advisory Group
802.9	Integrated Voice/Data Networks
802.10	Network Security
802.11	Wireless Networks
802.12	Demand Priority Access LAN, 100 Base VG - Any LAN

OSI Model Enhancements

The bottom two layers - Data Link and Physical - define how multiple computers can simultaneously use the network without interfering with each other.

Divides the Data-link layer in to the Logical Link Control and Media Access Control sub layers.
Logical Link Control

Defines logical interface points called Service Access Points (Sap’s). This Sap’s are used to transfer information to upper layers.
Manages error and flow control.

Media Access Control

Is responsible for delivering error-free data between two computers.
Communicates directly with the network adapter card and
Categories

802.12 define standards for both this sub layer and the Physical layer
802.3
802.4
802.5 and

Drivers

A device driver is software that tells the computer how to drive or work with the device so that the device performs the job it's supposed to.
Provide communication between a network adapter card and the redirector in the computer.
the Media Access Control driver is another name for the network card device driver
When installing a driver, you need to know these things

IRQ
I/O Port Address
Memory Mapped (Base Memory Address)
Transceiver Type

Drivers are called

Network Drivers,

MAC drivers,

NIC drivers.

Resides in the Media Access Control sub layer of the Data Link layer. Therefore, the NIC driver ensures direct communication between the computer and the NIC.

Packets

Special control information is added in order to:

disassemble packets
reassemble packets
check for errors

Data is broken down into smaller more manageable pieces called packets.

Types of data sent includes

Computer control data and commands and requests.
Original block of data is converted to a packet at the Transport layer.
Can contain information such as messages or files.
Session control codes such as error correction and retransmission requests.

Packet Components

Header

Alert signal to indicate packet is being transmitted
Source address.
Clock synchronization information.
Destination address.

Data

Varies from 512 to 4096 bytes (4K), depending on the network
Contains actual data being sent.

Trailer

Usually contains a CRC.
Content varies by protocol.

Packet Creation

Look at the example on pp. 201 - 204
Begins at the Application layer where data is generated.
Transport layer breaks the data into packets and adds sequencing information needed to reassemble data at the other end => the structure of the packets is defined by the common protocol being used between the two computers.
Data is passed through the Physical layer to the cable.
Each layer subsequently adds information to the packet; the corresponding layer on the receiving machine reads the information.

Packet Addressing

A broadcast type address gets attention of all computers on the network
Every NIC sees all packets sent on its cable segment but only interrupts the computer if the packet address matches the computer's address

Protocols

Protocols are rules and procedures for communication.

How Protocols Work

The Sending Computer

Breaks data into packets.
Prepares the data for transmission.
Adds addressing information to the packet

The Receiving Computer (same steps in reverse)

Strips the data from the packet.
Copies the data to a buffer for reassembly.
Takes the packet off the cable.
Passes the reassembled data to the application.

Protocol Stacks (or Suites)

Ensure that data is prepared, transferred, received and acted upon.
A combination of protocols, each layer performing a function of the communication process.

The Binding Process

Binding order dictates which protocol the operating systems uses first.
Binding also happens with the Operating System architecture: for example, TCP/IP may be bound to the NetBIOS session layer above and network card driver below it. The NIC device driver is in turn bound to the NIC.
Allows more than one protocol to function on a single network adapter card. (e.g. both TCP/IP and IPX/SPX can be bound to the came card

Standard Stacks

Novell NetWare
Apple AppleTalk
TCP/IP
ISO/OSI
IBM SNA (Systems Network Architecture)
Digital DECnet

Protocol types map roughly to the OSI Model into three layers:

Application Level Service Users

Application Layer

Session Layer
Presentation Layer

Transport Services

Transport Layer

Network Services

Network Layer
Data Link Layer
Physical Layer

Application Protocols

Work at the upper layer of the OSI model and provide application to application interaction and data exchange.

Examples:

APPC-IBM's peer to peer SNA protocol used on AS400's
FTAM: an OSI file access protocol.
SMTP: Internet e-mail.
FTP: Internet file transfer
SNMP: Internet network management protocol.
X.400: international e-mail transmissions.
NCP: Novell client shells or redirectors.
AppleTalk and AppleShare: Apple's protocol suite.
AFP: Apple's protocol for remote file access.
DAP (data access protocol): DECnet file access protocol.
X.500: file and directory services across systems.
Telnet: Internet protocol for logging on to remote hosts.
Microsoft SMB: client shells and redirectors.

Transport Protocols

These protocols provide communication sessions between computers and ensure data is moved reliably between computers.

Examples:

SPX (sequenced packet exchange): Novell protocol suite.
NWLink: Microsoft implementation of IPX/SPX.
NetBEUI: establishes communications sessions between computers and provides the underlying data transport services.
TCP (transmission control protocol): internet protocol for guaranteed delivery of sequenced data.
ATP, NBP: Apple's communication session and transport protocols.

Network Protocols

These provide link services

They also

handle

addressing and routing,
error checking and
Retransmission requests.

Define rules for Ethernet or Token Ring.

Examples:

IP (Internet Protocol): packet forwarding and routing.
NWLink: Microsoft implementation of IPX/SPX.
NetBEUI: Transport for NetBIOS sessions and applications.
IPX: (Internet work Packet Exchange): Novell's protocol for packet forwarding and routing.
DDP (datagram delivery protocol): An AppleTalk data transport protocol.

The IEEE protocols at the Physical Layer

802.3 (CSMA /CD - Ethernet)

Logical bus network.
Data is transmitted on the wire to every computer but only those meant to receive respond.
can transmit at 10 Mbps
CSMA /CD protocol listens and allows transmission when the wire is clear

802.4 (Token Passing)

bus layout that used token passing
token determines which computer can send
every computer receives all of the data but only the addressed computers responds

802.5 (Token Ring)

transmits at 4 Mbps or 16 Mbps
logical ring network; physical set up as star network
token determines which computer can send

Important Protocols

TCP/IP

Routable, defector standard for internetworking.
SMTP, FTP, SNMP are protocols written for TCP/IP
Provides communications in a heterogeneous environment.
Disadvantages are size and speed.

NetBEUI

Originally, NetBIOS and NetBEUI were tightly tied together but, NetBIOS has been separated out to be used with other routable protocols. NetBIOS acts as a tool to allow applications to interface with the network; by establishing a session with another program over the network.
NetBIOS extended user interface.
Compatible with most Microsoft networks.
NetBIOS operates at the Session layer.
Small, fast and efficient.
Not routable and compatible only with Microsoft networks.

X.25

Originally established to connect remote terminals to mainframe hosts.
Protocols incorporated in a packet switching network of switching services.

XNS

Xerox Network System.
Large, slow and produces a lot of broadcasts.
Developed for Ethernet LANs but has been replaced by TCP/IP.

IPX/SPX and NWLink

Small and fast.
Used for Novell networks.
Routable.

APPC

Designed to enable application programs running on different computers to communicate and exchange data directly.
Advanced Program to Program Communication
Developed by IBM to support SNA.

AppleTalk

Apple's proprietary protocol stack for Macintosh networks.

OSI Protocol Suite

each protocol maps directly to a single layer of the OSI model

DECnet

Defines communications over Ethernet, FDDI MAN's and WAN's.
DECnet can also use TCP/IP and OSI protocols as well as its own protocols.
Digital Equipment's proprietary protocol stack
Routable.

Putting data on the Cable

Access Methods

The 4 major methods

Carrier Sense Multiple Access Methods

With collision detection (CSMA/CD)
With collision avoidance (CSMA/CA).

Carrier Sense Multiple Access with Collision Detection. (CSMA/CD)

Computer senses that the cable is free.
Data is sent.
If data is on the cable, no other computer can transmit until the cable is free again.
If a collision occurs, the computers wait a random period of time and retransmit.

Known as a contention method because computers compete for the opportunity to send data. (Database apps cause more traffic than other apps)
This can be a slow method
More computers cause the network traffic to increase and performance to degrade.
The ability to "listen" extends to a 2,500 meter cable length => segments can't sense signals beyond that distance.
Token passing that allows only a singe opportunity to send data

A Demand Priority method

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)

All other computers wait until the data is sent.
The major drawback of trying to avoid network collisions is that the network traffic is high due to the broadcasting of the intent to send a message.
In CSMA/CA, the computer actually broadcasts a warning packet before it begins transmitting on the wire. This packet eliminates almost all collisions on the network because each computer on the network does not attempt to broadcast when another computer sends the warning packet.

Token Passing

Special packet is passed from computer to computer.
Original sending computer receives the acknowledgment and sends the token on.
NO collisions.
The token comes from the Nearest Active Upstream Neighbor and when the computer is finished, it goes to the Nearest Active Downstream Neighbor.
A computer that wants to transmit must wait for a free token.
Computer takes control of the token and transmits data. Only this computer is allowed to transmit; others must wait for control of the token.
Receiving computer strips the data from the token and sends an acknowledgment.
uses "beaconing" to detect faults => this method is fault tolerant
NO contention => equal access to all computers on the network.

Demand Priority

100 Mbps standard called 100VG-AnyLAN. "Hub- based".
Certain types of data are given priority if data reaches the repeater simultaneously. If two have the same priority, BOTH are serviced by alternating between the two.
Repeaters manage network access by performing cyclical searches for requests to send from all nodes on the network. The repeater or HUB is responsible for noting all addresses, links and end nodes and verifying if they are all functioning. An "end node" can be a computer, bridge, router or switch.

Advantages over CSMA/CD

Transmissions are through the HUB and are not broadcast to all other computers on the network.
There is only communication between the sending computer, the hub and the destination computer.
Computers Uses four pairs of wires which can send and receive simultaneously.

Other Methods

AppleTalk

The cabling system for an AppleTalk network is called Local Talk.
AppleTalk has a dynamic network addressing scheme.

During boot up, the AppleTalk card broadcasts a random number on the network as its card address. If no other computer has claimed that address, the broadcasting computer configures the address as its own. If there is a conflict with another computer, the computer will try to use different IP combinations until it finds a working configuration.

Local Talk uses CSMA/CA

ARC Net

ARC Net uses a token passing method in a logical ring similar to Token Ring networks.
However, a token is used to allow computers to speak in turn.

The token is not passed in a logical ring order because ARC Net does not use the ring topology; instead the token is passed to the next highest numerical station
Use DIP switches to set the number (the Station Identifier) of the workstations, which you want to be beside each other so the token is passed to the next computer efficiently.

However, the computers in an ARC Net network do not have to be connected in any particular fashion.

ARC Net can utilize a star, bus, or star bus topology.

Data transmissions are broadcast throughout the entire network, which is similar to Ethernet.
ARC Net isn't popular anymore => ARC Net speeds are a mere 2.5 Mbps.

Most important ARC Net facts for you to know:

It uses a logical-ring media access method.
ARC Net uses RG-62 (93 ohms) cabling;
It can be wired as a star, bus, or star bus; and

Summary Chart

Feature or Function	CSMA/CD	CSMA/CA	Token Passing	Demand Priority
Type of Communication	Broadcast-based	Broadcast-based	Token-based	Hub-based
Type of Access Method	Contention	Contention	Non-contention	Contention
Type of Network	Ethernet	Local Talk	Token Ring ARC net	100VG-AnyLAN

Networking Essentials Notes - Section 1

2009-07-04T17:50:00.004-04:00

Network Orientation

Peer to Peer Networks

No dedicated server or hierarchy also called a workgroup.
Limited growth.
Usually 10 or fewer workstations.
Computers are in same general area.
Users act as their own administrator and security.

Server Based Networks

Employs specialized servers.

File and Print
Application
Mail
Fax
Communications (gateways)

Central administration.
10 or more users.
Greater security.
Data Redundancy.
Supports many users
Centralized backup.

Combination Networks

Users can share resources among themselves as well as access server-based resources.
Combines the features of both Peer to Peer and Server based networks.

Network Topologies

There are 4 basic topologies with variations

Bus Topology

Data is sent to all computers on the trunk. Each computer examines EVERY packet on the wire to determine who the packet is for and accepts only messages addressed to them.
Bus consists of a single linear cable called a trunk.
Bus is a passive topology.
Repeaters can be used to regenerate signals.
But it’s difficult to isolate malfunctions and if the backbone goes down, the entire network goes down.
Usually uses Thinnet or Thicknet

both of these require 50 ohm terminator

Performance degrades as more computers are added to the bus.
Signal bounce is eliminated by a terminator at each end of the bus.
Barrel connectors can be used to lengthen cable.
good for a temporary, small (fewer than 10 people) network

Star Topology

Computers are connected by cable segments to a centralized hub.
If a computer goes down, the network functions normally.
Signal travels through the hub to all other computers.
Requires more cable.
most scalable and reconfigurable of all topologies
If hub goes down, entire network goes down.

Ring Topology

Computers are connected on a single circle of cable.
usually seen in a Token Ring or FDDI (fiber optic) network
Token passing is used in Token Ring networks. The token is passed from one computer to the next, only the computer with the token can transmit. The receiving computer strips the data from the token and sends the token back to the sending computer with an acknowledgment. After verification, the token is regenerated.
Relatively easy to install, requiring ;minimal hardware
Each computer acts as a repeater and keeps the signal strong => no need for repeaters on a ring topology
No termination required => because its a ring

Mesh

Meshes use a significantly larger amount of network cabling than do the other network topologies, which makes it more expensive.
The mesh topology is highly fault tolerant.

Every computer has multiple possible connection paths to the other com-putters on the network, so a single cable break will not stop network communications between any two computers.

The mesh topology connects each computer on the network to the others.

Star Bus Topology

No single computer can take the whole network down. If a single hub fails, only the computers and hubs connected to that hub are affected.
Several star topologies linked with a linear bus.

Star Ring Topology

This topology is popular for Token Ring networks because it is easier to implement than a physical ring, but it still provides the token passing capabilities of a physical ring inside the hub.
Also known as star wired ring because the hub itself is wired as a ring. This means it's a physical star, but a logical ring.
A single computer failure cannot stop the entire network, but if the hub fails, the ring that the hub controls also fails.
The passing of the token.
Just like in the ring topology, computers are given equal access to the network media through

Hybrid Mesh

A true mesh is expensive because of all the wire needed.
Most important aspect is that a mesh is fault tolerant.
Another option is to mesh only the servers that contain information that everyone has to get to. This way the servers (not all the workstations) have fault tolerance at the cabling level.

Connecting Network Components

Primary Cable Types

Coaxial Cable
Twisted-pair

UTP - Unshielded Twisted Pair
STP - Shielded Twisted Pair

Fiber-optic

Coaxial Cable

Consists of a solid or stranded copper core surrounded by insulation, a braided shield and an insulating jacket.

Plenum (fire resistant) graded cable can be used in false ceilings of office space or under the floor.
Both thin and thick cables can use (see pp. 80-81 for pics)

BNC cable connectors,
BNC barrel connectors
BNC T connectors
BNC terminators.

Braided shield prevents noise and crosstalk.
More resistant to interference and attenuation than twisted pair cabling.
Can transmit data, voice and video.
Offers moderate security ----> better than UTP/STP

Coaxial Cable Types

RG-8 and RG-11	Thicknet (50 ohms)
RG-58 Family
RG-58 /U	Solid copper (50 ohms)
RG-58 A/U	Thinnet, Stranded copper (50 ohms)
RG-58 C/U	Thinnet, Military grade (50 ohms)

RG-59	Broadband/Cable TV (75 ohm) video cable

Thinnet - RG-58 cable

called
0.25" thick.
Uses

BNC twist connector,
BNC barrel connectors
BNC T connectors
50 ohm terminators

Can carry signals 185 meters or 607 feet.
Types: (pics on page 78)

RG-62 A/U

ARCnet cable (93 ohm)
RG-62 A/U is the standard ARCnet cable, but ARCnet can use fiber optic or twisted pair.

Terminators are resistors that prevent signal bounce or echo.
Each cable must have a terminator whose impedance matches the cable type
Impedance = current resistance measured in ohms

Here are some limitations of 10Base2 Ethernet:

Length of trunk segment may be up to 607 feet.
Entire network trunk length can't exceed 3035 feet (925 meters)
The minimum cable length between workstations is 20 inches.
The Ethernet 5-4-3 Rule for connecting segments is 5 trunk segments can be connected, with 4 repeaters or concentrators, with no more than 3 populated segments (on coaxial cable).
A maximum of 30 workstations is allowed per trunk.
There may be no more than 1024 workstations per network.

Thicknet - RG-8 and RG-11 coaxial cable

Can carry signals 500 meters or 1640 feet.
much less flexible and far more bulky and harder to install than thinnet
better security than thinnet
Vampire taps are used to attach a transceiver to the thicknet trunk.
better resistance to electrical interference than thinnet.
MORE expensive than thinnet.
0.5" thick
used for 10Base5 networks, linear bus topology
transmits at 10 Mbps
Uses DIX or AUI (Attachment Unit Interface) connector - also known as DB-15 connector to connect to external transceivers.

Twisted-Pair Cable

Easy to install.
Uses RJ-45 telephone-type connectors (larger than telephone and consists of eight wires vs. Telephone's 4 wires).
Consists of two insulated copper wires twisted around each other.
Twisting cancels out electrical noise from adjacent pairs (crosstalk) and external sources.
Generally inexpensive.

Unshielded Twisted Pair (UTP)

Maximum cable length is 100 meters or 328 feet (10BaseT).
Types:

Cat 1 Voice grade telephone cable.
Cat 2 Data grade up to 4 Mbps, four twisted pairs.

Category 3 and above is needed for Ethernet networks. Cat 3, 4, and 5 use RJ-45 connectors

Cat 3 Data grade up to 10 Mbps, four pairs w/3 twists/ft.
Cat 4 Data grade up to 16 Mbps, four twisted pairs.
Cat 5 Data grade up to 100 Mbps, four twisted pairs.

This is the cheapest cable to put in. Exam questions ALWAYS take this as a given.

Here are some limitations of 10BaseT Ethernet:-

Workstations may be no more than 328 feet from the concentrator port.
The minimum cable length between workstations is 8 feet.
1,023 stations are allowed on a segment without bridging.

Other Drawbacks

easily tapped (because there is no shielding)
UTP is particularly susceptible to crosstalk, which is when signals from one line get mixed up with signals from another.
100 meters is shortest distance => attenuation is the biggest problem here.

Shielded Twisted Pair (STP)

Uses a woven copper braid jacket and a higher quality protective jacket. Also uses foil wrap between and around the wire pairs.
Shielding makes it somewhat harder to install.
Same 100 meter limit as UTP.
harder to tap
used in AppleTalk and Token Ring networks.
Much less susceptible to interference and supports higher transmission rates than UTP.

Fiber Optic Cable

Consists of a small core of glass or plastic surrounded by a cladding layer and jacket.
Most expensive and difficult to work with.
Immune to tapping.
Can transmit at 100 Mbps and way up to 2 GBPS.
Good for very high speed, long distance data transmission.
NOT subject to electrical interference.
Fibers are unidirectional (light only travels in one direction) so two fibers are used, one for sending and one for receiving. Kelvar fibers are placed between the two fibers for strength.
Up to 2000 meters without a repeater.
Supports data, voice and video.
Cable can't be tapped and data stolen => high security
Needs specialized knowledge to install => expensive all round.

Cable Type Comparisons
Type	Speed	Distance	Installation	Interference	Cost	# of nodes per segment	# of nodes per network
10BaseT	10 Mbps	100 meters	Easy	Highly susceptible	Least expensive	1 computer
100BaseT	100 Mbps	100 meters	Easy	Highly susceptible	More expensive than 10BaseT
STP	16 to 155 Mbps	100 meters	Moderately Easy	Somewhat resistant	More expensive than Thinnet or UTP
10Base2	10 Mbps	185 meters	Medium Difficulty	Somewhat resistant	Inexpensive	30	1024
10Base5	10 Mbps	500 meters	More difficult than Thinnet	More resistant than most cable	More expensive than most cable	100	300
Fiber Optic	100 Mbps to 2 GBPS	2000 meters	Most difficult	Not susceptible to electronic interference	Most expensive type of cable

Signal Transmission

Base band Transmission -- Digital

Flow is bi-directional. Some can transmit and receive at the same time.
Base band systems use repeaters to strengthen attenuated signals.
Base band transmission uses digital signaling over a single frequency.
Entire communication channel is used to transmit a single signal.

Broadband Transmission -- Analog

Signals are continuous and non-discrete.
Broadband uses analog signaling over a range of frequencies.
Flow is uni-directional and so two frequency channels or two separate cables must be used.

If this is the case, ALL devices must be tuned to use only certain frequencies.
If enough bandwidth is available, multiple analog transmission systems such as cable TV AND network transmissions can be on the same cable at the same time.

Uses Amplifiers for signal regeneration.

Helpful mnemonic to remember the difference:

Base band is "BEDR"

Bidirectional
Entire channel taken up
Digital
Repeaters used to strengthen signal

IBM Cabling

Connected with proprietary IBM unisex connectors.
Uses AWG standard wire size.
Defines cables as types

Type 1	STP (Shielded twisted-pair)	Used for computers and MAU's. 101 m	These three cable types can be used in Token Ring Networks	16 Mbps 260 computer limit
Type 2	STP, Voice and data	100 m
Type 3	UTP; Voice grade	45 m Most common Token Ring Cable		4 Mbps 72 computer limit
Type 5	Fiber-optic	industry standard
Type 6	STP Flat; Carpet grade	Limited to 1/2 the distance of Type 1 cable
Type 8	STP; Data patch	used to connect MSAU's together used to extend Type 3 cables from one computer to the MSAU
Type 9	STP; Plenum grade	used under floors or in ceiling space

Important Cabling Considerations

Installation Logistics

How easy is the cable to work with?

Shielding

Is the area "noisy"?
Do you need plenum grade cable => more expensive

Crosstalk

Power lines, motors relays and radio transmitters cause crosstalk
Where data security is important this is a problem

Transmission Speed (part of the bandwidth)

100 Mbps is becoming common
Fiber can go well over 100 Mbps but costs and requires experts to install.
Transmission rates are measured in Mbps
10 Mbps is common

Cost

Distance costs you money

Attenuation

Different cables can only transmit so far without causing too many errors

Wireless Local Area Networks

Used where cable isn't possible - remote sites; also when mobility is important.
Use transceivers or access points to send and receive signals between the wired and wireless network.

There are 4 techniques for transmitting data

Infrared transmission consists of four types;

Scatter: good within 100 ft.
Reflective
Line of sight
Broadband optical telephonic: used for multimedia requirements; as good as cable.

Laser requires direct line-of-sight.
Narrow-band (single frequency) radio

Cannot go through steel or load-bearing walls.
Limited to 4.8 Mbps.
Requires a service handler.

Spread-Spectrum Radio

Signals over a range of frequencies.
Quite slow; limited to 250 Kbps.
Uses hop timing for a predetermined length of time.
Coded for data protection.

Point to Point Transmission

Transfers data directly from PC to PC (NOT through cable or other peripherals)
Supports data rates from 1.2 to 38.4 Kbps up to

200 feet indoors or
1/3 of a mile with line of site transmission.

Uses a point to point link for fast error-free transmission.
Penetrates objects.
Also communicates with printers, bar code readers, etc.

Multipoint Wireless Bridge

Uses spread-spectrum radio to create a wireless backbone up to three miles.
Provides a data path between two buildings.

Long-Range Wireless Bridge

This costs less than T1, but T1 will transmit at 1.544 Mbps
Uses spread-spectrum technology to provide Ethernet and Token-Ring bridging for up to 25 miles.

Mobile Computing

Uses wireless public carriers to transmit and receive using;

Packet-radio communication.

Unlinked to satellite, broadcast only to device this has correct address.

Satellite stations.

Microwave, most common in USA, 2 X directional antennas, building to building, building to satellite

Cellular networks.

CDPD same as phone, sub second delays only, real time transmission, can tie into cabled network.

Slow transmission rate: 8 Kbps - 19.2 Kbps

Network Adapter Cards

The roles of the network Adapter card it to:

Prepare data from the computer for the network cable.
Control the flow of data between the computer and the cabling system.
Send the data to another computer.

LAN's contain hardware and firmware (software routines in ROM) programming that implements the

Media Access Control
Logical Link Control and

Functions of the Data Link layer of the OSI

Preparing Data

On network cable, data must travel in a single bit stream in what's called a serial transmission (b/c on bit follows the next).
Data moves along paths in the computer called a BUS - can be 8, 16, 32 bits wide.
card uses DMA (Direct Memory Access) where the computer assigns memory space to the NIC

if the the card can't move data fast enough, the card's buffer RAM holds it temporarily during transmission or reception of data

The transceiver is the component responsible for translating parallel (8, 16, 32-bit wide) into a 1 bit wide serial path.
A unique network address or MAC address is coded into chips in the card

Sending and Controlling Data

The LAN's of the two computers exchanging data agree on the following:

Maximum size of the groups of data being sent
The amount of time to wait before confirmation is sent
How much data each card can hold before it overflows
The amount of data to be sent before confirmation
The time intervals between send data chunks
The speed of the data transmission

Network Card Configuration

IRQ: a unique setting that requests service from the processor.

IRQ #	Common Use	I/O Address
IRQ 1	Keyboard
IRQ 2(9)	Video Card
IRQ 3	Com2, Com4	2F0 to 2FF
IRQ 4	Com1, Com3	3F0 to 3FF
IRQ 5	Available (Normally LPT2 or sound card )
IRQ 6	Floppy Disk Controller
IRQ 7	Parallel Port (LPT1)
IRQ 8	Real-time clock
IRQ 9	Redirected IRQ2	370 - 37F
IRQ 10	Available (maybe primary SCSI controller)
IRQ 11	Available (maybe secondary SCSI controller)
IRQ 12	PS/2 Mouse
IRQ 13	Math Coprocessor
IRQ 14	Primary Hard Disk Controller
IRQ 15	Available (maybe secondary hard disk controller)

Base I/O port: Channel between CPU and hardware

Each hardware device must have a different base I/O port
Specifies a channel through which information flows between the computer's adapter card and the CPU. Ex. 300 to 30F.

Base Memory address: Memory in RAM used for buffer area

Each device needs its own unique address.
some cards allow you to specify the size of the buffer ( 16 or 32 k, for example)
Identifies a location in the computer's RAM to act as a buffer area to store incoming and outgoing data frames. Ex. D8000 is the base memory address for the NIC.

Transceiver:

Use jumpers on the card to select which to use
Sometimes selected as on-board or external. External usually will use the AUI/DIX connector: Thicknet, for example

Data Bus Architecture

The NIC must

match the computer's internal bus architecture and
EISA (Extended Industry Standard Architecture): Introduced by consortium of manufacturers and offers a 32-bit data path.
Micro-Channel Architecture (MCA): Introduced by IBM in its PS/2 line. Functions as either 16 or 32 bit.
have the right cable connector for the cable being used

ISA (Industry Standard Architecture): original 8-bit and later 16-bit bus of the IBM-PC.
PCI (Peripheral Component Interconnect): 32-bit bus used by Pentium and Apple Power-PC's. Employs plug and play.

Improving Network Card Performance

Direct Memory Access (DMA):

Data is moved directly from the network adapter card's buffer to computer memory.

Shared System Memory:

The network adapter selects a portion of the computer's memory for its use.
MOST common

RAM buffering:

Ram on the adapter card acts as a buffer that holds data until the CPU can process it.
this keeps the card from being a bottleneck

Shared Adapter Memory:

Network adapter card contains memory which is shared with the computer.
The computer identifies RAM on the card as if it were actually installed on the computer

Bus Mastering:

The adapter card takes temporary control of the computer's bus, freeing the CPU for other tasks.
moves data directly to the computer's system memory
Available on EISA and MCA
can improve network performance by 20% to 70%

On-board microprocessor:

enables the adapter card to process its own data without the need of the CPU

Wireless Adapter Cards

Used to create an all-wireless LAN
uses a wireless concentrator, which acts as a transceiver to send and receive signals
Add wireless stations to a cabled LAN

Remote-Boot PROMS (Programmable Read Only Memory)

Enables diskless workstations to boot and connect to a network.
Used where security is important.

Networking Essentials Notes - Section 1

2009-07-04T17:48:00.001-04:00

Network Orientation
Peer to Peer Networks
No dedicated server or hierarchy also called a workgroup.
Limited growth.
Usually 10 or fewer workstations.
Computers are in same general area.
Users act as their own administrator and security.
Server Based Networks
Employs specialized servers.
File and Print
Application
Mail
Fax
Communications (gateways)
Central administration.
10 or more users.
Greater security.
Data Redundancy.
Supports many users
Centralized backup.
Combination Networks
Users can share resources among themselves as well as access server-based resources.
Combines the features of both Peer to Peer and Server based networks.

Network Topologies
There are 4 basic topologies with variations
Bus Topology
Data is sent to all computers on the trunk. Each computer examines EVERY packet on the wire to determine who the packet is for and accepts only messages addressed to them.
Bus consists of a single linear cable called a trunk.
Bus is a passive topology.
Repeaters can be used to regenerate signals.
But it’s difficult to isolate malfunctions and if the backbone goes down, the entire network goes down.
Usually uses Thinnet or Thicknet
both of these require 50 ohm terminator
Performance degrades as more computers are added to the bus.
Signal bounce is eliminated by a terminator at each end of the bus.
Barrel connectors can be used to lengthen cable.
good for a temporary, small (fewer than 10 people) network
Star Topology
Computers are connected by cable segments to a centralized hub.
If a computer goes down, the network functions normally.
Signal travels through the hub to all other computers.
Requires more cable.
most scalable and reconfigurable of all topologies
If hub goes down, entire network goes down.
Ring Topology
Computers are connected on a single circle of cable.
usually seen in a Token Ring or FDDI (fiber optic) network
Token passing is used in Token Ring networks. The token is passed from one computer to the next, only the computer with the token can transmit. The receiving computer strips the data from the token and sends the token back to the sending computer with an acknowledgment. After verification, the token is regenerated.
Relatively easy to install, requiring ;minimal hardware
Each computer acts as a repeater and keeps the signal strong => no need for repeaters on a ring topology
No termination required => because its a ring
Mesh
Meshes use a significantly larger amount of network cabling than do the other network topologies, which makes it more expensive.
The mesh topology is highly fault tolerant.
Every computer has multiple possible connection paths to the other com-putters on the network, so a single cable break will not stop network communications between any two computers.
The mesh topology connects each computer on the network to the others.

Star Bus Topology
No single computer can take the whole network down. If a single hub fails, only the computers and hubs connected to that hub are affected.
Several star topologies linked with a linear bus.

Star Ring Topology
This topology is popular for Token Ring networks because it is easier to implement than a physical ring, but it still provides the token passing capabilities of a physical ring inside the hub.
Also known as star wired ring because the hub itself is wired as a ring. This means it's a physical star, but a logical ring.
A single computer failure cannot stop the entire network, but if the hub fails, the ring that the hub controls also fails.
The passing of the token.
Just like in the ring topology, computers are given equal access to the network media through
Hybrid Mesh
A true mesh is expensive because of all the wire needed.
Most important aspect is that a mesh is fault tolerant.
Another option is to mesh only the servers that contain information that everyone has to get to. This way the servers (not all the workstations) have fault tolerance at the cabling level.

Connecting Network Components
Primary Cable Types
Coaxial Cable
Twisted-pair
UTP - Unshielded Twisted Pair
STP - Shielded Twisted Pair
Fiber-optic

Coaxial Cable
Consists of a solid or stranded copper core surrounded by insulation, a braided shield and an insulating jacket.
Plenum (fire resistant) graded cable can be used in false ceilings of office space or under the floor.
Both thin and thick cables can use (see pp. 80-81 for pics)
BNC cable connectors,
BNC barrel connectors
BNC T connectors
BNC terminators.
Braided shield prevents noise and crosstalk.
More resistant to interference and attenuation than twisted pair cabling.
Can transmit data, voice and video.
Offers moderate security ----> better than UTP/STP

Coaxial Cable Types
RG-8 and RG-11
Thicknet (50 ohms)
RG-58 Family

RG-58 /U
Solid copper (50 ohms)
RG-58 A/U
Thinnet, Stranded copper (50 ohms)
RG-58 C/U
Thinnet, Military grade (50 ohms)

RG-59
Broadband/Cable TV (75 ohm) video cable

Thinnet - RG-58 cable
called
0.25" thick.
Uses
BNC twist connector,
BNC barrel connectors
BNC T connectors
50 ohm terminators
Can carry signals 185 meters or 607 feet.
Types: (pics on page 78)

RG-62 A/U
ARCnet cable (93 ohm) RG-62 A/U is the standard ARCnet cable, but ARCnet can use fiber optic or twisted pair.
Terminators are resistors that prevent signal bounce or echo.
Each cable must have a terminator whose impedance matches the cable type
Impedance = current resistance measured in ohms
Here are some limitations of 10Base2 Ethernet:
Length of trunk segment may be up to 607 feet.
Entire network trunk length can't exceed 3035 feet (925 meters)
The minimum cable length between workstations is 20 inches.
The Ethernet 5-4-3 Rule for connecting segments is 5 trunk segments can be connected, with 4 repeaters or concentrators, with no more than 3 populated segments (on coaxial cable).
A maximum of 30 workstations is allowed per trunk.
There may be no more than 1024 workstations per network.
Thicknet - RG-8 and RG-11 coaxial cable
Can carry signals 500 meters or 1640 feet.
much less flexible and far more bulky and harder to install than thinnet
better security than thinnet
Vampire taps are used to attach a transceiver to the thicknet trunk.
better resistance to electrical interference than thinnet.
MORE expensive than thinnet.
0.5" thick
used for 10Base5 networks, linear bus topology
transmits at 10 Mbps
Uses DIX or AUI (Attachment Unit Interface) connector - also known as DB-15 connector to connect to external transceivers.

Twisted-Pair Cable

Easy to install.
Uses RJ-45 telephone-type connectors (larger than telephone and consists of eight wires vs. Telephone's 4 wires).
Consists of two insulated copper wires twisted around each other.
Twisting cancels out electrical noise from adjacent pairs (crosstalk) and external sources.
Generally inexpensive.
Unshielded Twisted Pair (UTP)
Maximum cable length is 100 meters or 328 feet (10BaseT).
Types:
Cat 1 Voice grade telephone cable.
Cat 2 Data grade up to 4 Mbps, four twisted pairs.
Category 3 and above is needed for Ethernet networks. Cat 3, 4, and 5 use RJ-45 connectors
Cat 3 Data grade up to 10 Mbps, four pairs w/3 twists/ft.
Cat 4 Data grade up to 16 Mbps, four twisted pairs.
Cat 5 Data grade up to 100 Mbps, four twisted pairs.
This is the cheapest cable to put in. Exam questions ALWAYS take this as a given.
Here are some limitations of 10BaseT Ethernet:-
Workstations may be no more than 328 feet from the concentrator port.
The minimum cable length between workstations is 8 feet.
1,023 stations are allowed on a segment without bridging.
Other Drawbacks
easily tapped (because there is no shielding)
UTP is particularly susceptible to crosstalk, which is when signals from one line get mixed up with signals from another.
100 meters is shortest distance => attenuation is the biggest problem here.
Shielded Twisted Pair (STP)
Uses a woven copper braid jacket and a higher quality protective jacket. Also uses foil wrap between and around the wire pairs.
Shielding makes it somewhat harder to install.
Same 100 meter limit as UTP.
harder to tap
used in AppleTalk and Token Ring networks.
Much less susceptible to interference and supports higher transmission rates than UTP.

Fiber Optic Cable
Consists of a small core of glass or plastic surrounded by a cladding layer and jacket.
Most expensive and difficult to work with.
Immune to tapping.
Can transmit at 100 Mbps and way up to 2 GBPS.
Good for very high speed, long distance data transmission.
NOT subject to electrical interference.
Fibers are unidirectional (light only travels in one direction) so two fibers are used, one for sending and one for receiving. Kelvar fibers are placed between the two fibers for strength.
Up to 2000 meters without a repeater.
Supports data, voice and video.
Cable can't be tapped and data stolen => high security
Needs specialized knowledge to install => expensive all round.
Cable Type Comparisons
Type
Speed
Distance
Installation
Interference
Cost
# of nodes per segment
# of nodes per network
10BaseT
10 Mbps
100 meters
Easy
Highly susceptible
Least expensive
1 computer

100BaseT
100 Mbps
100 meters
Easy
Highly susceptible
More expensive than 10BaseT

STP
16 to 155 Mbps
100 meters
Moderately Easy
Somewhat resistant
More expensive than Thinnet or UTP

10Base2
10 Mbps
185 meters
Medium Difficulty
Somewhat resistant
Inexpensive
30
1024
10Base5
10 Mbps
500 meters
More difficult than Thinnet
More resistant than most cable
More expensive than most cable
100
300
Fiber Optic
100 Mbps to 2 GBPS
2000 meters
Most difficult
Not susceptible to electronic interference
Most expensive type of cable

Signal Transmission
Base band Transmission -- Digital
Flow is bi-directional. Some can transmit and receive at the same time.
Base band systems use repeaters to strengthen attenuated signals.
Base band transmission uses digital signaling over a single frequency.
Entire communication channel is used to transmit a single signal.
Broadband Transmission -- Analog
Signals are continuous and non-discrete.
Broadband uses analog signaling over a range of frequencies.
Flow is uni-directional and so two frequency channels or two separate cables must be used.
If this is the case, ALL devices must be tuned to use only certain frequencies.
If enough bandwidth is available, multiple analog transmission systems such as cable TV AND network transmissions can be on the same cable at the same time.
Uses Amplifiers for signal regeneration.
Helpful mnemonic to remember the difference:
Base band is "BEDR"
Bidirectional Entire channel taken up Digital Repeaters used to strengthen signal
IBM Cabling
Connected with proprietary IBM unisex connectors.
Uses AWG standard wire size.
Defines cables as types
Type 1
STP (Shielded twisted-pair)
Used for computers and MAU's.
101 m
These three cable types can be used in Token Ring Networks
16 Mbps
260 computer limit
Type 2
STP, Voice and data
100 m

Type 3
UTP; Voice grade
45 m
Most common Token Ring Cable
4 Mbps
72 computer limit
Type 5
Fiber-optic
industry standard

Type 6
STP Flat; Carpet grade
Limited to 1/2 the distance of Type 1 cable

Type 8
STP; Data patch
used to connect MSAU's together
used to extend Type 3 cables from one computer to the MSAU

Type 9
STP; Plenum grade
used under floors or in ceiling space

Important Cabling Considerations
Installation Logistics
How easy is the cable to work with?
Shielding
Is the area "noisy"?
Do you need plenum grade cable => more expensive
Crosstalk
Power lines, motors relays and radio transmitters cause crosstalk
Where data security is important this is a problem
Transmission Speed (part of the bandwidth)
100 Mbps is becoming common
Fiber can go well over 100 Mbps but costs and requires experts to install.
Transmission rates are measured in Mbps
10 Mbps is common
Cost
Distance costs you money
Attenuation
Different cables can only transmit so far without causing too many errors

Wireless Local Area Networks
Used where cable isn't possible - remote sites; also when mobility is important.
Use transceivers or access points to send and receive signals between the wired and wireless network.
There are 4 techniques for transmitting data
Infrared transmission consists of four types;
Scatter: good within 100 ft.
Reflective
Line of sight
Broadband optical telephonic: used for multimedia requirements; as good as cable.

Laser requires direct line-of-sight.
Narrow-band (single frequency) radio
Cannot go through steel or load-bearing walls.
Limited to 4.8 Mbps.
Requires a service handler.
Spread-Spectrum Radio
Signals over a range of frequencies.
Quite slow; limited to 250 Kbps.
Uses hop timing for a predetermined length of time.
Coded for data protection.
Point to Point Transmission
Transfers data directly from PC to PC (NOT through cable or other peripherals)
Supports data rates from 1.2 to 38.4 Kbps up to
200 feet indoors or
1/3 of a mile with line of site transmission.
Uses a point to point link for fast error-free transmission.
Penetrates objects.
Also communicates with printers, bar code readers, etc.
Multipoint Wireless Bridge
Uses spread-spectrum radio to create a wireless backbone up to three miles.
Provides a data path between two buildings.
Long-Range Wireless Bridge
This costs less than T1, but T1 will transmit at 1.544 Mbps
Uses spread-spectrum technology to provide Ethernet and Token-Ring bridging for up to 25 miles.
Mobile Computing
Uses wireless public carriers to transmit and receive using;
Packet-radio communication.
Unlinked to satellite, broadcast only to device this has correct address.
Satellite stations.
Microwave, most common in USA, 2 X directional antennas, building to building, building to satellite

Cellular networks.
CDPD same as phone, sub second delays only, real time transmission, can tie into cabled network.
Slow transmission rate: 8 Kbps - 19.2 Kbps

Network Adapter Cards

The roles of the network Adapter card it to:
Prepare data from the computer for the network cable.
Control the flow of data between the computer and the cabling system.
Send the data to another computer.
LAN's contain hardware and firmware (software routines in ROM) programming that implements the
Media Access Control
Logical Link Control and
Functions of the Data Link layer of the OSI
Preparing Data
On network cable, data must travel in a single bit stream in what's called a serial transmission (b/c on bit follows the next).
Data moves along paths in the computer called a BUS - can be 8, 16, 32 bits wide.
card uses DMA (Direct Memory Access) where the computer assigns memory space to the NIC
if the the card can't move data fast enough, the card's buffer RAM holds it temporarily during transmission or reception of data
The transceiver is the component responsible for translating parallel (8, 16, 32-bit wide) into a 1 bit wide serial path.
A unique network address or MAC address is coded into chips in the card
Sending and Controlling Data
The LAN's of the two computers exchanging data agree on the following:
Maximum size of the groups of data being sent
The amount of time to wait before confirmation is sent
How much data each card can hold before it overflows
The amount of data to be sent before confirmation
The time intervals between send data chunks
The speed of the data transmission
Network Card Configuration
IRQ: a unique setting that requests service from the processor.
IRQ #
Common Use
I/O Address
IRQ 1
Keyboard

IRQ 2(9)
Video Card

IRQ 3
Com2, Com4
2F0 to 2FF
IRQ 4
Com1, Com3
3F0 to 3FF
IRQ 5
Available (Normally LPT2 or sound card )

IRQ 6
Floppy Disk Controller

IRQ 7
Parallel Port (LPT1)

IRQ 8
Real-time clock

IRQ 9
Redirected IRQ2
370 - 37F
IRQ 10
Available (maybe primary SCSI controller)

IRQ 11
Available (maybe secondary SCSI controller)

IRQ 12
PS/2 Mouse

IRQ 13
Math Coprocessor

IRQ 14
Primary Hard Disk Controller

IRQ 15
Available (maybe secondary hard disk controller)

Base I/O port: Channel between CPU and hardware
Each hardware device must have a different base I/O port
Specifies a channel through which information flows between the computer's adapter card and the CPU. Ex. 300 to 30F.
Base Memory address: Memory in RAM used for buffer area
Each device needs its own unique address.
some cards allow you to specify the size of the buffer ( 16 or 32 k, for example)
Identifies a location in the computer's RAM to act as a buffer area to store incoming and outgoing data frames. Ex. D8000 is the base memory address for the NIC.
Transceiver:
Use jumpers on the card to select which to use
Sometimes selected as on-board or external. External usually will use the AUI/DIX connector: Thicknet, for example
Data Bus Architecture
The NIC must
match the computer's internal bus architecture and
EISA (Extended Industry Standard Architecture): Introduced by consortium of manufacturers and offers a 32-bit data path.
Micro-Channel Architecture (MCA): Introduced by IBM in its PS/2 line. Functions as either 16 or 32 bit.
have the right cable connector for the cable being used
ISA (Industry Standard Architecture): original 8-bit and later 16-bit bus of the IBM-PC.
PCI (Peripheral Component Interconnect): 32-bit bus used by Pentium and Apple Power-PC's. Employs plug and play.
Improving Network Card Performance
Direct Memory Access (DMA):
Data is moved directly from the network adapter card's buffer to computer memory.
Shared System Memory:
The network adapter selects a portion of the computer's memory for its use.
MOST common
RAM buffering:
Ram on the adapter card acts as a buffer that holds data until the CPU can process it.
this keeps the card from being a bottleneck
Shared Adapter Memory:
Network adapter card contains memory which is shared with the computer.
The computer identifies RAM on the card as if it were actually installed on the computer
Bus Mastering:
The adapter card takes temporary control of the computer's bus, freeing the CPU for other tasks.
moves data directly to the computer's system memory
Available on EISA and MCA
can improve network performance by 20% to 70%
On-board microprocessor:
enables the adapter card to process its own data without the need of the CPU
Wireless Adapter Cards
Used to create an all-wireless LAN
uses a wireless concentrator, which acts as a transceiver to send and receive signals
Add wireless stations to a cabled LAN
Remote-Boot PROMS (Programmable Read Only Memory)
Enables diskless workstations to boot and connect to a network.
Used where security is important.

2008-06-16T05:16:00.003-04:00

Hardware: (computer science) the mechanical, magnetic, electronic, and electrical components making up a computer system.

Computer hardware is the physical part of a computer,(not to be confused with software which is not physical) including the digital circuitry, as distinguished from the computer software that executes within the hardware.

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

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.

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!

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 .

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 mouse pad or desk.

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.

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.

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.