Data Representation

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Binary

  • Binary consists of 1 and 0s and is known as base 2
  • It is similar to counting in denary (base 10) but the values from right to left increase by a power of 2 
  • Binary is used to store information on computers and it allows them to peform complex calculation quickly.
  • Each Binary digit is known as a bit
  • 8 bits=1 byte
  • 4 bits=1 nibble/Half byte
  • When converting  binary, you need to draw out a table with the value 1,2,4,8,16,32,64,128 going from left to right
  • Place 1s and 0s in the columns and then add the values
  • When converting from denary to binary,draw the table and move from the left to the right subtracting teh amount each time.Put 1 in columns that give positive answers.
  • When adding with binary,work from right to left and carry the ones over.
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Hexadecimal Numbers

  • Hexidecimal is known as base 16 and it goes from 1 - F(15)
  • It is a quicker and easier way of writing down binary values 
  • It uses the numbers 1-9 and then after 9, it goes from A- F 
  • When converting binary into hex, split it from the right side into 4 bits 
  • Then put 8,4,2,1 and then convert into denary but use the letters A-F after 10 
  • When converting from hex to binary, multiply the numbers by 4096,256,16 and then add them together
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Adding with binary

  • 0+0=1
  • 0+1=1
  • 1+1=10
  • 1+1+1=11
  • 1+1+1+1=100
  • You should always start adding from the right side 
  • Carry the result overs if the answer is 2 digits 
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ASCII

  • ASCII stands for American Standard Code for Information Interchange 
  • It is used represent letters and symbols as numbers
  • Each character is given a unique number from 0-127
  • It uses 7 bits to encode 128 characters 
  • Some use 8 bits which gives them 256 characters 
  • The extra characters are used to represent non-Englisg characters,graphics symbols and mathematical symbols 
  • Most computers use ASCII codes to represent text which makes it possible for computers to communicate easily with each other.
  • A=0100 0000
  • a=0110 0001
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Unicode

  • Unicode uses 16 to 32 bits and is usually shown in hexadecimal
  • It has a much larger set as it uses more bits to represent mpore characters 
  • It alllows character sets from other languages
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Lossy and Lossless

  • Files can be compressed in two ways: lossy and lossless
  • Lossy is when the compression of the file cause it to lose quality. 
  • A common way is to reduce the colour depth from 24 bits to 8. This causes the image to look more granulated or have unusual colour blocks.
  • JPEGand MP3 are lossy file compression
  • An advantage of lossy is that it greatly reduces the file size and is used more commonly.However, a lot of data is lost permenantly and it cant be used on text or software files.
  • Lossless compression is when data is temporarily removed to decrease its file size
  • Instead of sending the pixels individually,they are sent in blocks.
  • Data is only temporarily removed so no quality is losta nd the files can be decompressed. However,there is only a slight reduction in file size so a lot of space will still be used up. 
  • Examples of lossless files are PNG,FLAC and TIFF
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Images

  • Bitmaps are the name given to one way of storing graphics on a computer system.It is laid out in a grid with each box containing one PIxel (Picture Element)
  • Pixelated - when the image is made up of large blocks rather than smooth lines.It happens to small or poor quality images copied from the internet when you try to make it larger
  • To get more detailed images , you could use a larger grid.
  • The colour depth is the number of bits per pixel
  • You can work out the amount of colours you get by doing 2 to the power of bits per pixel.
  • Most images use 24 bit colour depth with 8 bits to indicate the levels of red, green and blue.
  • File Size = The size of grid*colour depth 
  • Resoloution describes how big the pixels are in the image. A higher resolution leads to better image quality. It is usually meausred in pixels per inch .
  • Higher resoloution will increase the file size.
  • Meta data is at the beginning of  a file and it tells the computer how to process the dat. Meta data includes the size of the image,colour depth, resoloution and file size.
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Sound

  • Sound is recorded as an analogue signal. These are signals which are continually changing 
  • This is converted into a digital sound using an analogue to digital converter.It is converted into binary.
  • The amplitude of the sound wave is ampled at a regular rate. THis is known as sample rate.
  • Sampling intervals - the gaps between each of the points where the recording is ampled
  • Sample Rate- how many samples you take in a second measure in kHZ
  • Sample size - the number of bits for each sample
  • Bit rate = Sampling frequency *sample size
  • Increasing the sample rate will liead to a better quality which will match the recording more closely.
  • Increasing the sample size means quiter noises are picked up
  • Increasing the bit rate will lead to a bigger file.
  • Waveform Audio - Standard audio file format. IT produces CD quality sound files but the files are very large
  • MPEG-1 Audio Layer - It gets rid of portions of ausio that are inaudible to the human ear
  • Ogg Vorbis - data is compressed at a variable rate.
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Assembly Language

  • Computer memory is split into numbered section which can be referred back to in instructions
  • Assembly language is very simple programming that humans can understand and computers cane reas.The machine uses binary for these instructions. The machine code is made up of the op code and the data
  • HALT - stps the promgramme -1110 0000
  • STORE - saves value in memory location - 0100
  • ADD- Adds value from memory box - 0110
  • LOAD -loads the memory box - 0011 
  • ADD # - adds specific value - 0111
  • SUB - 1000
  • SUB# - 1001
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