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... y files to the systems hard disk; also it allows video play back of higher quality to be run from the drive. A CDROM works by projecting a very thin beam of light called a laser at the surface of the disk. The disk that the drive is reading is covered in tiny pits, a little like that of a vinyl record, these pits are used to represent the data on the disk.
Where there is a pit on the disk the drive will read this as a binary 1 and where there is not a pit, the drive will read this as a 0. It is now possible to get CD writers, these new drives are just the same as the ROM version but also have the ability to write data to special CDs that allow writing to them. This is useful when transferring larger files between computers that have no other means of data swapping. Speakers Speakers when connected to a suitable sound card allow the user of the system to hear sounds. The sound maybe warning bleeps emitted by the system to say something is wrong i. e.
A message warning the user they are about to over write a file, this message is normally accompanied by a beep to alert the user. Speakers can also be used to hear music CDs, digital audio files or the sounds that are in a game etc. Modem A modem is a means of connecting a system to other systems or to the World Wide Web. Once a network connection has been established it is then possible to transferee data across this connection. The speed at which data can be sent is all dependant on what modem hardware is installed and the line it is connected to. Standard modems can transferee data at speeds of 56 kb a second, this is quite slow for transferring larger files of 2 mb plus. 56 K modems use analogue phone lines to transferee data, analogue lines are prone to noise on them so can cause errors when transferring data.
Newer modem technology is now available this is called ADSL. An ADSL modem uses a digital line to transferee the data instead of an analogue modem. The advantage of digital modems over analogue is that there is only an ON and an OFF state, this means that it is highly unlikely that the data will become corrupted in transit. Tape drives Tape drives are used primarily for back of important system information.
Often an image of the entire hard disk will be saved on this device so that, in the case of total system failure, the image can be transferred back to the disk allowing the system to return to an earlier point in time where it was working correctly. Tape drives can store massive amounts of data (the tape drive in the picture below can store 66 GB of data on a single tape), this is why they are suitable for back up of whole hard disk drives. However the speed at which a tape drive stores data to its media is not very fast (6 MB/sec), it may take an hour or so to transferee the contents of an entire hard disk to tape. Pixels A pixel is the smallest single dot of coloured light that is individually controllable by the monitor.
The word pixel is a combination of the words picture and element. This refers to the individual dots that, when grouped, comprise a video display's picture. If you look very close at the monitor screen you can see the individual pixels. A monitor is graded on its ability for clarity, the way that the clarity is improved is by fitting higher numbers of smaller pixels into a square inch. The way this is measured is by the monitors dot pitch, generally. 25 mm or. 28 mm. The dot pitch indicates a higher quality tube (CRT or Cathode Ray Tube) with sharper dot (pixel) resolution.
Attributes The attributes that are associated with VDUs can be said to be things such as the resolutions (height x width), colour depth, type of screen and positioning. The resolution of the display will generally be stated as either 640 x 480, 800 x 600, 1024 x 768 or 1600 x 1200. These different resolutions allow the VDU to display a higher quality output due to the amount of dots per inch or DPI. As the resolution is increased so does the available work space (see below) As you can see from the picture on the left the icons are a lot smaller and the task bar is very long due to the fact that a resolution of 1280 x 1024 is being used.
The screen dump on the right shows what can be seen on the screen when a resolution of 640 x 480 is used. The red dotted line shows the smaller screens equivalent size. Color depth is also a screen attribute, a CRT monitor can display up 32 bit color. This means 32, 000 colors can be on the screen at anyone time. This makes pictures look a lot clearer and more colorful. (See below: notice the blue aura around the hand of the lady, the 16 -colour picture has large blocks of color that are used to fill areas that would normally have a smooth transition of color to give a clearer image) The type of screen can be classed as Color, green, or black and white.
Color monitors have now pretty much-phased out Green screens and black and white displays have gone almost entirely. Character code ASCII ASCII (pronounced Ass-key) is a standard character representation code that is recognized world-wide. ASCII stands for American standard code for information interchange. It represents characters by using seven single bits to make up a byte, i. e.
this would define its characters being only 7 bits in length, not 8. Each character is assigned a number between 0 and 127 this gives 128 different characters. As almost all PCs and Macintosh use ASCII data can easily be transferred between them with out and converting between character sets. All displays are able to display this code on them, an example of this would be when using word processors.
The characters are converted from their binary ASCII value into a character on the screen. EBCDIC IBM adopted EBCDIC from punched card codes in the early 1960 s and still uses it on mainframes. It exists in at least six versions and has features such as non-contiguous letter sequences, control code values from 0 to 63, and the absence of several ASCII punctuation marks. However, when transferring data to or from IBM syst...
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