← Years 9–10 Data & Information

Redundancy: repeated data that can be shortened

Repeated or predictable data, like a run of the same letter or colour, that can be stored in a shorter form without losing any information.

Part of: 9-10 Digital Technologies: Data compression — Module 6, IGCSE Computer Science 0478 — 1.3 Data Storage and Compression — Module 39, ACARA Digital Technologies Years 9–10 — Data Compression — Module 15

Understanding Redundancy: repeated data that can be shortened in Years 9–10 Data & Information

What it does: Eight blue pixels in a row (B for blue) repeat the same colour, so this is redundancy that could be stored as 8B. Noticing six Ws in a row lets you write 6W instead, which is shorter but gives the same information. The string of repeated A's is predictable, so it can be stored in a shorter form such as 10A. The random letters have no pattern to shorten. Long runs of identical pixels are redundant, so they can be described in a short form. A busy photo has far less repetition. 6W still tells us there were exactly six W's. Shortening redundant data this way keeps all of the information.

Common mistakes: The text only has 4 A's, but the next line says A repeats 5 times. The line should be text ← AAAAABBB so the repeated data matches the short form 5A3B. The row shows only 3 red pixels, but the next line says R repeats 4 times. The row should be R R R R B B.

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Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 6–16) and word search (Modules 6–132).

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Learning
Duo
Which string has more redundancy?
AAAAAAAAAAQXZPLMWEBN
Matches
ABCDEFGH can be shortened a lot because it has lots of redundancy
↓
There are no repeats or patterns in ABCDEFGH, so it has no redundancy to remove
Applying
Meanings
Term
redundancy
Meaning
Repeated or predictable data, like a run of the same letter or colour, that can be stored in a shorter form without losing any information.
Practice
Text: AAAAABBBCCCCCC
Testing
Gaps
AAAAAAAA is stored as A
Check Answer
Spots
1text ← AAAABBB
2A repeats 5 times

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Quick Questions

1. Which string has more redundancy?
A. QXZPLMWEBN
B. AAAAAAAAAA ✓
The string of repeated A's is predictable, so it can be stored in a shorter form such as 10A. The random letters have no pattern to shorten.
2. What is redundancy in data?
A. Repeated or predictable data that can be shortened ✓
B. Data that has been deleted by mistake
Redundancy is not a mistake or lost data. It is repetition or predictability that lets us store the same information in less space.
3. Which image would have the most redundancy?
A. A plain blue sky with every pixel the same colour ✓
B. A photo of a crowded market with thousands of colours
Long runs of identical pixels are redundant, so they can be described in a short form. A busy photo has far less repetition.
4. When we remove redundancy by writing WWWWWW as 6W, what happens to the information?
A. Some is lost, because we can no longer tell how many W's there were
B. None is lost, because we can rebuild WWWWWW ✓
6W still tells us there were exactly six W's. Shortening redundant data this way keeps all of the information.
5. Which is an example of spotting a pattern to shorten data?
A. Writing ABABABAB as 4 x AB ✓
B. Deleting every second letter of ABABABAB
Finding the repeating pattern lets us describe it in a shorter way. Deleting letters would throw information away.

Match the Pairs

AAAAAAAAAA → A run of repeated characters: redundant data that could be stored in a shorter form
10A → A shortened form of a repeated run that keeps all the information
A row of pixels that are all the same colour is redundant data → BBBBBBBB
Spotting a pattern lets you store repeated data in fewer characters → WWWWWW -> 6W
ABCDEFGH can be shortened a lot because it has lots of redundancy → There are no repeats or patterns in ABCDEFGH, so it has no redundancy to remove
AAAAA shortened to 5 (the letter is dropped) → The letter was lost, so the information is gone; it should be 5A

Key Term

redundancy
Repeated or predictable data, like a run of the same letter or colour, that can be stored in a shorter form without losing any information.

Fill in the Blanks

1. AAAAAAAA is stored as 8A
Hint: Type the number of times the letter repeats
2. Repeated or predictable data is redundancy
Hint: Type the term for repeated or predictable data that can be shortened
3. WWWWWWBB -> 6W2B
Hint: Type the pixel colour letter that repeats in the first run
4. ABABABAB = 4 x AB
Hint: Type the repeating pattern that can be shortened
5. row = RRRRRRRRRR short = 10R
Hint: Type the count of repeated red pixels in the row

Spot the Error

Question 1
A text ← AAAABBB
B A repeats 5 times
C B repeats 3 times
D short ← 5A3B
Line A — The text only has 4 A's, but the next line says A repeats 5 times. The line should be text ← AAAAABBB so the repeated data matches the short form 5A3B.
Question 2
A row ← R R R B B
B R is repeated 4 times
C B is repeated 2 times
Line A — The row shows only 3 red pixels, but the next line says R repeats 4 times. The row should be R R R R B B.
Question 3
A pixels ← W W W W W W
B all pixels are the same
C store ← 5W
Line C — There are 6 white pixels in a row, so the short form must be 6W. Writing 5W would lose information when the data is rebuilt.
Question 4
A msg ← ZZZZZZ
B count ← 9
C short ← 6Z
Line B — The message contains 6 Z's, so the count should be 6. A wrong count would not match the short form 6Z.
Question 5
A data ← ABABABAB
B pattern ← AB
C repeat ← 2 times
D short ← AB x 4
Line C — The pattern AB appears 4 times in ABABABAB, not 2. Spotting the pattern and counting its repeats correctly is what lets us shorten it to AB x 4.

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