[1.1]
Analogue Data & Digital Data
Analogue Data
Data that is physically represented.
Analogue data varies continuously identifies each tone of what is being measured.
Examples
• Our voices
• The sound coming from any acoustic instrument
• Lines (gaps) on a vinyl record.
• Shade on a sun dial.
Digital Data
Digital data is a combination of numbers 1 or 0.
Computers use digital data to represent data.
Examples
• Digital storage of sound
• Sampling measures the sound level several times per second and records this as binary digits.
Graphics
Black and white bitmap graphics use bit (1 or 0) to represent white (0) and black (1) dots.
The dots are called pixels.
It is possible to represent 256 colours by using a byte (8 bits) for each pixel.
Sound
To represent analogue sound as digital data, the sampling process is used.
Sampling is where hardware, such as a microphone, measures the sound level (sampling resolution) several times per second (sample rate) and records this as binary digits.
Conversion
An analogue-digital (A/D) converter is an electronic circuit that converts continuous signals into discrete digital numbers. To intercept the signal back, it reverses the process.
A digital-analogue (D/A) converter is an electronic circuit for converting a digital signal to an analogue signal (current, voltage or electrical charge).
Data type | Analogue Data | Digital Data |
Advantages | As continuous data is stored, there is no deterioration in the quality of the data. | Storage of data in digital form requires less physical space, as digital storage devices are smaller (compare vinyl disk against a memory stick). |
Disadvantages | Analogue data can deteriorate when it is copied or transmitted as a result of signal corruption from recording equipment. | As a result of data being sampled, the data is not recorded as a whole, as a result, digital data may be less accurate and of lower quality than analogue data. |
[1.2]
Storing Data Digitally
Capacity
Computer systems can only store and process binary digits, also known as BITs.
A BIT is either a 1 or a 0.
When 8 bits are stored as a binary number, they are collectively called a byte.
BITs
1 Byte: 8 BITs
Half a Byte, so 4 BITs, is called a ‘Nybble’.
Capacity
As storage increases, we need units.
We use the prefixes below.
1024 x 1024 bytes =
1,048,576 bytes
VERY large units.
So, less likely to be asked about.
Lossless compression
Lossless compression uses an algorithm that compresses data into a form that may be decompressed at a later time, without any loss of data, returning the file to its exact original form.
It is preferred to lossy compression, when the loss of any detail, for example in a computer program or a word-processed document, could have a detrimental effect.
Original file | |
Pixel coordinates | Colour |
0,0 | Transparent |
0,1 | Transparent |
0,2 | Transparent |
0,3 | Transparent |
0,4 | Transparent |
0,5 | Transparent |
0,6 | Transparent |
0,7 | Transparent |
0,8 | Transparent |
0,9 | Transparent |
Etc - 256 rows in total! | |
Compressed file | |
Pixel coordinates | Colour |
0,0 - 1,6 / 1,15 / etc. | Transparent |
1,7 - 1,14 / 2,4 / etc. | Red |
2,5 / 3,4 - 3,5 / 3,8 / etc. | White |
2,6 - 2,7 / 3,6 - 3,7 / etc. | Blue |
Lossy Compression
Lossy compression is a technique that compresses the file size by discarding some of the data.
The technique aims to reduce the amount of data that needs to be stored.
Compression Ratio
The compression ratio is calculated using the simple formula below:
NOTE:
You are permitted to have a calculator with you in the exam, in case a question like this appears.
Secondary storage
This technology is used in hard disks and tapes. Data is stored on a magnetic medium, which can be a disc or a tape, by writing data using a write-head. Data can then be read by the read-head.
Solid state technology is used in storage media such as flash memory sticks. The technology is called solid state as it doesn’t have any moving parts, such as a read-head in magnetic storage.
Magnetic
Solid state
A storage method where data is transmitted and stored on remote storage systems, where it is maintained, managed, and backed up over a network - usually the internet. Consumers generally pay for their cloud data storage at a monthly price per capacity. Although we say ‘the cloud’ the data is stored on hard disks or SSDs on a remote site.
Cloud
Optical storage media uses technology such as lasers. Laser beams are projected onto a CD/ DVD or Blu-ray disc and if light is reflected back, then data is read as a 1. If light is not reflected back, data is read as a 0. Lasers are used to read and write information on a disk.
Optical
[3.1]
Digital Communication Methods
Emailing
Compare with the traditional post
Social networking websites and apps
Blogs
Instant messaging
Video conferencing
Internal and external methods of communication for businesses
Internal and external methods of communication for businesses
Promotion