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24 Dec 2025
•
GCSE Computer Science: U3 Data Representation Notes
mirs
@miralmaoo
1 / 5
Number Systems and Data Basics
Every piece of information on your computer - whether it's a photo, song, or text - gets converted into binary code using just 0s and 1s. Think of binary as the computer's native language, whilst we humans prefer decimal (base 10) for everyday counting.
Hexadecimal (base 16) acts as a brilliant shortcut for programmers. Instead of writing out long strings of binary digits, hex lets you represent four binary digits with just one character. It's faster to type, easier to remember, and way less likely to contain errors when you're coding.
Memory sizes follow a simple pattern: 1 byte equals 8 bits, and from there it scales up - kilobytes, megabytes, gigabytes, and terabytes. Converting between these number systems becomes straightforward once you understand the place values: in binary, each position represents powers of 2 (1, 2, 4, 8, 16...).
Quick tip: Remember "Make Great Toys" for MB, GB, TB - it'll help you recall the order of memory units!
Binary Operations and Character Encoding
Binary addition follows simple rules, but watch out for that carry bit when 1+1=0 (carry 1). Binary shifts are your mathematical shortcuts: shifting left doubles a number, whilst shifting right halves it. These operations are lightning-fast for computers to perform.
Character sets like ASCII and Unicode give every letter, number, and symbol a unique binary code. ASCII started with 128 characters using 7 bits, but that wasn't nearly enough for global communication. Unicode expanded this massively using 16 bits, accommodating everything from Korean characters to your favourite emojis.
The beauty of these systems is their logical organisation - numbers, letters, and symbols are grouped together in sequence, making it predictable to work with. ASCII remains a subset of Unicode, so older systems still work perfectly with newer ones.
Remember: When adding binary numbers, overflow errors occur when your result exceeds the available bits - the extra data simply disappears!
Image Representation
Digital images are made up of tiny squares called pixels, and each pixel stores colour information as binary data. A bitmap image is essentially a massive grid of these pixels, with file formats like JPEG, PNG, and GIF storing this data in different ways.
Colour depth determines how many colours each pixel can display - more bits per pixel means more colour combinations and better image quality. The formula is simple: 2^n colours, where n is the number of bits. So 8 bits gives you 256 different colours per pixel.
File size calculations are straightforward: width × height × colour depth ÷ 8 gives you the size in bytes. Higher resolution and greater colour depth create stunning images, but they'll eat up your storage space quickly.
Don't forget about metadata - the invisible information about your image like when it was created, camera settings, and file format. This data doesn't count towards the basic file size calculation, but it's stored alongside your image.
Pro tip: Understanding these calculations helps you balance image quality against file size - crucial for web design and digital media work!
Sound Representation and Compression
Sound waves are analogue by nature, but computers need digital data to work with them. This conversion happens through sampling - measuring the sound's amplitude at regular intervals, like taking thousands of snapshots per second of a constantly changing wave.
Sampling rate (measured in Hertz) and sample resolution (bits per sample) determine your audio quality. Higher values create more accurate digital representations of the original sound, but they also create much larger files. The trade-off between quality and storage space is constant in digital media.
Data compression tackles this storage problem through two main approaches. Lossy compression (like MP3) permanently removes some data to shrink file sizes, whilst lossless compression (like PNG) rearranges data more efficiently without losing anything.
Run Length Encoding is a clever lossless technique that replaces repeated data with frequency/data pairs. It works brilliantly with images that have large areas of the same colour, but it can actually increase file sizes when there aren't many repeating patterns.
Key insight: The file size formula is sampling rate × sample resolution × duration - this helps you predict how much storage your audio projects will need!
Advanced Compression Techniques
Huffman coding represents one of the most elegant compression algorithms you'll encounter. It works by giving shorter binary codes to frequently used characters and longer codes to rare ones, dramatically reducing overall file size whilst maintaining perfect data integrity.
Looking at the example with "SHE SELLS SEA SHELLS", Huffman coding achieves a 65% reduction in file size compared to standard ASCII encoding. The most common letters like 'E' and 'S' get the shortest codes, whilst less frequent characters receive longer binary representations.
This technique proves particularly effective with text that has predictable patterns - English text, programming code, and structured data all compress beautifully. The algorithm builds a custom code tree for each file, ensuring optimal compression for that specific content.
The beauty of Huffman coding lies in its mathematical precision - there's no guesswork involved, and the original data can always be perfectly reconstructed. This makes it ideal for situations where losing even a single bit would be catastrophic.
Amazing fact: Huffman coding is so efficient that it's used in popular formats like JPEG and MP3, often as part of more complex compression systems!
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
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This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
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Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
GCSE Computer Science: U3 Data Representation Notes
mirs
@miralmaoo
Data representation is all about how computers store and process the information we use every day - from text messages to photos to music. Understanding how computers convert everything into binary code (just 0s and 1s) is crucial for computing,... Show more
Number Systems and Data Basics
Every piece of information on your computer - whether it's a photo, song, or text - gets converted into binary code using just 0s and 1s. Think of binary as the computer's native language, whilst we humans prefer decimal (base 10) for everyday counting.
Hexadecimal (base 16) acts as a brilliant shortcut for programmers. Instead of writing out long strings of binary digits, hex lets you represent four binary digits with just one character. It's faster to type, easier to remember, and way less likely to contain errors when you're coding.
Memory sizes follow a simple pattern: 1 byte equals 8 bits, and from there it scales up - kilobytes, megabytes, gigabytes, and terabytes. Converting between these number systems becomes straightforward once you understand the place values: in binary, each position represents powers of 2 (1, 2, 4, 8, 16...).
Quick tip: Remember "Make Great Toys" for MB, GB, TB - it'll help you recall the order of memory units!
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Binary Operations and Character Encoding
Binary addition follows simple rules, but watch out for that carry bit when 1+1=0 (carry 1). Binary shifts are your mathematical shortcuts: shifting left doubles a number, whilst shifting right halves it. These operations are lightning-fast for computers to perform.
Character sets like ASCII and Unicode give every letter, number, and symbol a unique binary code. ASCII started with 128 characters using 7 bits, but that wasn't nearly enough for global communication. Unicode expanded this massively using 16 bits, accommodating everything from Korean characters to your favourite emojis.
The beauty of these systems is their logical organisation - numbers, letters, and symbols are grouped together in sequence, making it predictable to work with. ASCII remains a subset of Unicode, so older systems still work perfectly with newer ones.
Remember: When adding binary numbers, overflow errors occur when your result exceeds the available bits - the extra data simply disappears!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Image Representation
Digital images are made up of tiny squares called pixels, and each pixel stores colour information as binary data. A bitmap image is essentially a massive grid of these pixels, with file formats like JPEG, PNG, and GIF storing this data in different ways.
Colour depth determines how many colours each pixel can display - more bits per pixel means more colour combinations and better image quality. The formula is simple: 2^n colours, where n is the number of bits. So 8 bits gives you 256 different colours per pixel.
File size calculations are straightforward: width × height × colour depth ÷ 8 gives you the size in bytes. Higher resolution and greater colour depth create stunning images, but they'll eat up your storage space quickly.
Don't forget about metadata - the invisible information about your image like when it was created, camera settings, and file format. This data doesn't count towards the basic file size calculation, but it's stored alongside your image.
Pro tip: Understanding these calculations helps you balance image quality against file size - crucial for web design and digital media work!
Sign up to see the contentIt's free!
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Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Sound Representation and Compression
Sound waves are analogue by nature, but computers need digital data to work with them. This conversion happens through sampling - measuring the sound's amplitude at regular intervals, like taking thousands of snapshots per second of a constantly changing wave.
Sampling rate (measured in Hertz) and sample resolution (bits per sample) determine your audio quality. Higher values create more accurate digital representations of the original sound, but they also create much larger files. The trade-off between quality and storage space is constant in digital media.
Data compression tackles this storage problem through two main approaches. Lossy compression (like MP3) permanently removes some data to shrink file sizes, whilst lossless compression (like PNG) rearranges data more efficiently without losing anything.
Run Length Encoding is a clever lossless technique that replaces repeated data with frequency/data pairs. It works brilliantly with images that have large areas of the same colour, but it can actually increase file sizes when there aren't many repeating patterns.
Key insight: The file size formula is sampling rate × sample resolution × duration - this helps you predict how much storage your audio projects will need!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Advanced Compression Techniques
Huffman coding represents one of the most elegant compression algorithms you'll encounter. It works by giving shorter binary codes to frequently used characters and longer codes to rare ones, dramatically reducing overall file size whilst maintaining perfect data integrity.
Looking at the example with "SHE SELLS SEA SHELLS", Huffman coding achieves a 65% reduction in file size compared to standard ASCII encoding. The most common letters like 'E' and 'S' get the shortest codes, whilst less frequent characters receive longer binary representations.
This technique proves particularly effective with text that has predictable patterns - English text, programming code, and structured data all compress beautifully. The algorithm builds a custom code tree for each file, ensuring optimal compression for that specific content.
The beauty of Huffman coding lies in its mathematical precision - there's no guesswork involved, and the original data can always be perfectly reconstructed. This makes it ideal for situations where losing even a single bit would be catastrophic.
Amazing fact: Huffman coding is so efficient that it's used in popular formats like JPEG and MP3, often as part of more complex compression systems!
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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4.9/5
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4.8/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user