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Archive for August, 2010

Bandwidth

The amount of data which can be transmitted within a fixed time period.

bps – Bits per second

kbps – kilobits per second

mbps – Megabits per second

*USB pushes data through faster than serial*

Simplex – One way transmission

Half-duplex – Data goes both ways but only one way at a time

Full-duplex – Data can go both ways at the same time. 100mbps full-duplex means a bandwidth of 100 mbps in both directions.

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Scanners

Interfaces and cables are generally the same as printers, parallel, USB, SCSI and firewire

All-in-one

Multiple uses eg scanner, printer, copier and fax.

Low cost, easy to install

One upgrade for all devices

One port for all devices

Issues

One problem effects all devices and it is not designed for heavy use

Flatbed

Often used to scan books and phontos for archieving.

Can have a sheet feeder which will feeders to be scanned into the scanner although this will make the scan quality not as good.

Printers

A computer needs an interface with a printer to use it, common interfaces are

Serial – Slow data transfer

Parallel – Faster transfer than serial

Small Computer System Interface (SCSI) – Uses parallel technology

Universal Serial Bus (USB) – Fast and practical, PnP

Firewire/ i.LINK/ IEEE1394 – Fast data transfer

Ethernet – Connect the printer to a network using the RJ-45

Wireless – Infrared, Bluetooth or Wi-Fi, need transmitters and will work for a maximum of 3.7m

Laser

High quality

Fast from 20-30 ppm up to 100’s of ppm

Toner cartrige is cheaper pp

Impact

Uses printer tape or inked ribbon.

Noisy, slow, bad graphic quality and limited colour

Ink jet

Thermal, steams the ink onto the paper

Piezoelectric, Vibrates the ink onto the paper

Solid ink printers

Heats solid ink sticks and sprays it onto the paper, expensive to buy and run

Thermal printers

uses a special paper that turns black when heated

Dye-sublimation printers

Same as solid ink printer but it steams the ink onto the paper

When selecting a printer the following should be considered depending on the situation

Capacity and speed

Colour

Quality

Reliability

Warrenty

Sceduled servicing

Meat time between failures (MTNF)

Total cost of ownership

Networks

The advantages of networks are numerous they save money because only one printer, scanner or backup device is needed between multiple computers, files and memory can be shared between machines, files can also be made read only so they can’t be corrupted.

Software liecences are cheaper for networks than single computers and the administration is centralised so a program can be loaded onto multiple computers at once.

LAN (Local area network)

A group of computers under one administrative control

WAN (Wide area network)

A WAN connects LANs in different geographical areas, the internet is an example of this.

WLAN (Wireless LAN)

Wireless devices are used to connect computers

There are two main network types

Peer to peer

Each user controls their own machine and decides what others can see and use eg printers

When someone uses your information etc, they use your machine which impacts your memory.

Best to use with 10 or less machines

Client/server networks

The client or host computer request information or services from the server. The server provides the information or service

Network interface cards (NIC) must have the following info

Protocols – Must be the same between computers working on the same network.

IP address – Must be unique to each device, can be manually configured or automatically configured using DHCP

MAC address – Assigned by the manufacturer, can’t be changed.

 

Preventitive maintanance for networks

Keep things clean and clear

Check for wear and tear

Label both ends of wires

Check wireless connection strength

Use ipconfig tool to check network configurations

Trouble shooting

Unplug and replug

Reboot

login under different name

Use PING

Backing up files

Restore point

When the computer crashes the OS can rollback to a restore point.

Only OS and app file will be restored

Make sure you run an antivirus before creating a restore

You should create a restore point before updating or replacing the OS, when an app or driver is installed, manually at any time.

Backup tools

This is like a restore for data.

When backing up you only need to back up the stuff that has changed

Types of backup

Normal backup backs up files since forever.

Copy backup

Differentual backup takes longer but restoring is effectively one click.

Incremental backup backs up files since last backup, faster but restoring is slower because you have to restore every single increment

Daily backup

Ethernet

802.2

802.3

802.11x

Cabled ethernet

End stations listen for a clear line and then send. If no one is sending data the transmission succeeds, if someone is sending data there is a collision and the transmission wont work.

10BASE-T

10 Mbps

Baseband transmission

Twisted pair cabling

Uses star topology

100BASE-TX

Tx means it can take copper and fiber optic

1000Base-TX

Fast enough for live video

You can have several different bases on a network

Wi-Fi

802.11a

54 Mbps

5GHz radio frequency

30m range

80211b

2.4 GHz

11Mbps

30m range at 90m only 1Mbps

Interference from cordless phones, microwaves or bluetooth.

802.11g

54Mbps

2.4GHz

Compatible with 802.11b

30m range

works with a, b or g

802.11n

theortically 540 Mbps

2.4 or 5 GHz

50m range

LAN physical topologies

There are several ways computers can be compiled to communicate with each other.

Bus, Ring, Star, Hieracal star, Mesh

BUS

Each computer connects to a common cable, the cable connects one computer to the next, the ends of the cable have a terminator installed to prevent signal reflections and network errors. Only one computer can transmit data at a time otherwise collisions will occur and be destroyed. Bus is rarely used today.

RING

Hosts are connected in a circle, since there is no beginning or end it doesn’t need a terminator, a token (like a train) travels around the ring picking up information and dropping it off, if a computer has information it will give it to the token when it stops by, the token only delivers one piece of information at a time.

STAR

Has a central device, hub switch or router in the middle which information travels through to get from one computer to another. Hosts all connect directly connect into the central point. Uses more cable but if something goes down the system doesn’t and the problem is easier to find.

HIERACAL STAR

A network with several star setups.

MESH

Connects every (or almost) computer to every other one. The internet is one also used in wan. Cable failure doesn’t affect the network. Uses alot of cable. Packets are sent through in set sizes, the computer accepts these and puts them into order.

There is broadcast topology (send to everyone) and token topology(sends to intended host).

IEEE 802- institute of electrical and electronics engineers, established 1884 non-profit association, does standards for electronics and computers.

ansi and iso too

FDDI Fiber distributed data interface, runs on fiber-optics

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