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ICT revision

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10atvarghese 8T

on 19 September 2013

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Transcript of ICT revision

ICT Revision
Input Devices
An input device is any hardware device that can send any data to the computer. Without input devices a computer could only be a display device and the user would not be able to interact with it. They are split into 2 categories - Manual input devices and automatic devices.
Fact of the Day
Christopher Sholes purposely selected a physical layout that was difficult to type, so that typing speeds would be reduced! This was needed to reduce the jamming of "hammers" used to create individual letters on manual typewriters.
These are used to digitize images of pages or objects.
A light moves slowly over the surface of the picture or object to be scanned. The colors of the reflected light are detected and digitized to build up a digital image. The digital data can then be saved by a computer as an image file.

Optical Mark Reader (OMR)
OCR detects the presence of pencil marks by reflecting light onto it. Less light is reflected where the mark has been made. OMR systems are suited to reading pre-printed forms and check boxes such as National Lottery number selection sheets and multiple choice exam papers.

It is a fast method of inputting large amounts of data- up to 10000 forms per hour.
Only one computer needed to process the information
Possibility of missing data in the scanning process.
Incorrectly or unnumbered pages can lead to them being scanned in the wrong order.
Here is a video on Input devices
Keyboards allow a computer user to input letters, numbers, and other symbols into a computer and is what allows you to write an e-mail.The Function keys or F1 through F12 keys are used in programs as shortcut keys to performed frequently performed tasks. For example, the F1 key is the key to open the online help for most programs. Many keyboard are called qwerty keyboards. Some of the advantages are :
Reliable for data input of text and numbers.
Usually supplied with a computer so no additional cost.
Specialist keyboards are available eg. ergonomic gaming keyboards.
Some of the disadvantages are :
Users may be slow for not very accurate typists.
Disabled people may find keyboards difficult to use
Users may be slow for not very accurate typists

Flat-bed scanners are very accurate and can produce images with a far higher resolution than a digital camera
Can accurately capture an image but the original source may be more important than the scanned image.
Specialist scanners can convert old material such as 35mm negatives into digital files
Can produce very large image files which need a lot of computer memory to view and edit
Images use some quality in the digitizing process.
The quality of the final image is dependent on the quality of the original image.
Output Devices
Almost all computers have a monitor. Monitors are also known as Visual Display Units (VDUs). Most computers use this display as the main output device. There are two different types of display :

Desktop Monitors : These work in much the same way as a television set. They are bulky but fairly cheap to buy. e.g. £150 for a 14" screen.

Liquid Crystal Displays (LCDs) : These displays are completely flat and so can be used in portable computers and other small devices such as calculators. In ten years time LCDs will probably replace bulky desktop monitors.
The three most important features of a screen are its size, the colours it can display and its resolution. They apply to both desktop monitors and LCDs.

A CRT monitor is an old style of TV set or computer monitor. Known for their bulky style.

Size : How big is the screen ? Typical sizes are 10" or 12" for LCDs and 14", 15" or 21" for desktop monitors. The size is measured along the diagonal from the bottom left hand corner to the top right hand corner of the screen.

Colour : Is the monitor colour or black & white ? Most new desktop computers have colour screens as they are no longer that much more expensive than black & white ones and modern computer applications work better with a colour monitor.

Resolution : An image displayed on the screen is made up of lots of dots called pixels. If you look closely at the screen you may be able to see these pixels. The resolution of the screen is how many pixels there are up and down and from left to right across the screen. A variety of different resolutions are available. For PCs these resolutions have names. e.g. VGA is 640 x 480. This means that there are 640 pixels in each row across the screen and 480 pixels in each column up and down the screen.

Advantages of LCD over CRT-
LCD monitors with Energy Star ratings use little electricity in comparison to CRT machines as LCDs consume 25 watts to 50 watts, while CRT monitors consume 60 watts to 80 watts
LCD monitors are smaller, thinner and weigh half as much as CRTs. This allows you to mount an LCD on a wall or an arm.
An LCD monitor's tilt, swivel, height and orientation from horizontal to vertical can all be adjusted easily.
LCD monitors don't produce the flicker that CRTs do, generating less eye strain.
LCDs display text much more clearly than CRTs

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.

Headphones give sound output from the computer. They are similar to speakers, except they are worn on the ears so only one person can hear the output at a time. They are connected by cable or wireless. A transducer converts the electronic signals from the device into sounds which can then be heard by the user.
The sounds can only be heard by the user so you don't have to disturb anyone.
Lightweight and easy to carry around
Can listen to music on the move
Not everyone can listen to music
Storage Devices
What are Storage devices
Information and documents are stored in a computer storage so that it can be retrieved whenever they are needed later on.
Computer storage is the holding of data in an electromagnetic form for access by a computer processor
The processor, or central processing unit (CPU), is the brain of the computer. The more powerful the processor is, the faster your PC will run. The speed of a processor – that is the number of instructions per second that it can carry out - is measured in gigahertz (GHz).
Also consider the number of cores. A multi-core processor effectively has more than one CPU on a single silicon chip, so it’s better able to handle multiple tasks at once. Most modern desktops have multi-core processors.
When buying a new PC, for a basic machine you’ll need a dual-core processor that runs at about 2.5GHz - this will handle everyday basic computing tasks.

PC memory (Ram)
Random access memory (Ram) is your desktop computer’s short-term memory (the hard drive is used for long-term storage). Ram stores information when you’re using the computer - the amount determines the number of different tasks a PC carry out simultaneously.
Aim for as much Ram as you can afford. All modern desktop PCs will ship with at least 1GB of Ram, but aim for 2GB or more. Older versions of Windows weren’t able to handle large amounts of Ram, but this is no longer a problem with the latest 64-bit version of Windows 7 (assuming you have a 64-bit processor).
It’s possible to add more Ram to your computer. If you’re happy opening up your PC’s case and tinkering with it, this is one of the more straightforward and cheap ways of upgrading performance.

Stored by manufacture
Store instructions permanently
Fast but uses very little power.

Hard Disc
Computer hard disk drive
The computer’s hard disk drive provides long-term storage for your data – anything you save here will still be available even if you switch off the PC.
Until recently, hard drives were measured in gigabytes (GB), but now it’s not unusual to see terabyte (TB) hard drives (1TB is 1,024GB) when buying a new PC.
If you’re storing a lot of photos, videos and music, you can quickly eat into your free hard drive space, and the same is true if you install lots of big programs. However, large capacity drives aren’t too expensive.

External Hard drive
There are several different kinds of external hard disk.
The ones that you're likely to be most familiar with are the standalone drives which attach to and sit alongside your computer.
However, you can also get portable hard disks. These are generally smaller than the standalone drives both in terms of physical size and capacity. These are ideal for transferring files between computers.
Another advantage of a portable drive is that it’s possible to keep your data separate from your computer. Most businesses back up their data and keep their backup off site.
Ideally, we should all do the same – keep a copy of important data (treasured photos, say) in case of fire or theft, for example. You might find a copy on CD or DVD kept at a friend’s place would be just as good, though.
If you have a home network, you could consider a network hard disk which you can connect to your network so everyone can save their files onto it.
The speed of a drive on your network will be directly affected by the slowest part of your network – eg your wifi connection or your router. For this reason, the speed of these drives is less of an issue and ease of set up and use should be a more important consideration.

Desktop PCs will usually come with a CD/DVD drive of some sort. The most common drives let you read and write both CDs and DVDs, so you can back up your data to either of these discs.
DVDs hold lots more data than CDs, and are ideal for backing up big files.However, when choosing the best desktop PC, you might want to consider one with a drive that can read Blu-ray discs. These discs can store a lot of data, including high-definition films.
Blu-ray writers are also now available, and useful if you want to create your own Blu-ray movies from your high-definition video footage - but they’re expensive at the moment.

A memory stick is 'pen top' sized USB device and can be used in a similar way to a floppy disk but it is inserted into the USB port - it is then seen by the computer as a removable drive. They typically come in sizes from 512MB to 32GB upwards depending on the price paid.
Memory sticks can hold large quantities of data.
They are extremely portable, so the user can take them wherever they go.
They're durable, because they have no moving parts.

Portable storage devices in general are more likely to be lost, stolen or damaged

Memory Card
A memory card is a stamp-sized USB device and can be used in a similar way to a floppy disk but it is inserted into either a memory card reader or a USB converter - it is then seen by the computer as a removable drive. They typically come in sizes from 1 GB to 32 GB upwards, depending on the price paid. There are many available memory card formats, but since 2010 the SD card became the more favoured format.

Memory cards can hold large quantities of data.
They are extremely portable so the user can take them wherever they go.
Digital accessories such as compact cameras and mobile phones are able to read and write to memory cards allowing the user to transport large collections of photographs, songs or information with them.
They're durable because they have no moving parts.

Memory cards, specifically the micro SD card, are the smallest storage devices available. This means they are more likely to be lost, stolen or damaged.
All computers do not come with memory card readers built in. Users will often be required to purchase a card reader or USB converter to view the data on a card.

Printer-is a computer peripheral which produces a hard copy (text, graphic)
Laser printers are quite expensive to buy and run but produce a high quality output and are quiet and fast.
Ink-jet printers offer black and white or colour printing with reduced levels of quality and speed. Colour ink jet printers are cheaper to buy than colour laser printers.
Dot matrix printers are not so common today. They are comparatively noisy and low quality but are cheap to run and are used when carbon copies or duplicates need to be made, such as for wage slips. Also, they are useful in dirty environments such as a garage because they are much sturdier than the other two types of printer.
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