← IGCSE Computer Science Paper 1

Why compression is needed: less storage space

Compressed files are smaller, so they take up less storage space. This means more photos or songs fit on a device, and less storage needs to be bought.

Part of: IGCSE Computer Science 0478 — 1.3 Data Storage and Compression — Module 30, ACARA Digital Technologies Years 9–10 — Data Compression — Module 12, QCE Digital Solutions Unit 4 — Digital Methods for Exchanging Data — Module 52

Understanding Why compression is needed: less storage space in IGCSE Computer Science Paper 1

What it does: 8 GiB is 8192 MiB, and dividing by a 4 MiB compressed song gives 2048 songs. The smaller the file, the more songs fit. Subtracting the compressed size from the uncompressed size shows the storage saved, so less storage needs to be bought. Compression makes files smaller. Smaller files take up less storage space, so more files fit on the same device. 80 ÷ 2 = 40 compressed photos. Only 80 ÷ 8 = 10 uncompressed photos would fit, so compression lets four times as many photos fit. Comparing the two sizes shows how much storage compression saves: 5 MiB is 1/4 of 20 MiB.

Common mistakes: The number of files that fit is found by dividing the storage by the compressed size (compressed), not the original photo size. It should be count = storage // compressed. Compression makes files smaller, which is why they take up less storage space. The comment should say smaller, not larger.

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Learning

Duo

A phone has 64 GiB of storage. Which statement is true about compressing its photos?

Compressed photos are larger, so fewer of them fit on the phoneCompressed photos are smaller, so more of them fit on the phone

Matches

Compression makes files bigger, so fewer photos fit on a phone.

↓

Compression makes files smaller, not bigger. Smaller files mean more photos fit on the phone.

Applying

Meanings

Term

compression saves storage

Meaning

Compressed files are smaller, so they take up less storage space. This means more photos or songs fit on a device, and less storage needs to be bought.

Practice

originalSize ← 8

Testing

Gaps

IF compressedSize originalSize THEN

Check Answer

Spots

3compressed = 1

4count = storage // photo

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Quick Questions

1. A phone has 64 GiB of storage. Which statement is true about compressing its photos?

A. Compressed photos are larger, so fewer of them fit on the phone

B. Compressed photos are smaller, so more of them fit on the phone ✓

Compression makes files smaller. Smaller files take up less storage space, so more files fit on the same device.

2. Which is a reason for compressing a file to save storage space?

A. The file takes up more space but loads faster

B. The file takes up less space on the device ✓

Saving storage space means the compressed file is smaller than the original.

3. A music app stores 1000 songs. If each song is compressed, what happens to the total storage needed?

A. It goes down ✓

B. It goes up

Each compressed song is smaller, so the total storage needed for all 1000 songs goes down.

4. A company stores millions of images on its servers. How does compression help with cost?

A. Less storage needs to be bought, so costs are lower ✓

B. More storage needs to be bought, so costs are lower

Smaller files mean less storage capacity is needed. Buying less storage lowers the cost.

5. A photo is 8 MiB uncompressed and 2 MiB compressed. How many compressed photos fit in 80 MiB?

A. 40 photos ✓

B. 10 photos

80 ÷ 2 = 40 compressed photos. Only 80 ÷ 8 = 10 uncompressed photos would fit, so compression lets four times as many photos fit.

Match the Pairs

Uncompressed: 20 MiB, Compressed: 5 MiB → The compressed file is four times smaller, so it uses only a quarter of the storage space.

64 GiB / 4 GiB = 16 files → Dividing the storage by a file size gives how many files fit on the device.

Compression makes each song smaller, so more songs fit on a phone with 8 GiB of storage. → 8 GiB / 4 MiB = 2048 songs

Compression saves storage space, so a smaller and cheaper storage device can be bought. → Saved space = 20 MiB - 5 MiB = 15 MiB

Compression makes files bigger, so fewer photos fit on a phone. → Compression makes files smaller, not bigger. Smaller files mean more photos fit on the phone.

Compressed 5 MiB file + 20 MiB original = storage saved 25 MiB → The storage saved is found by subtracting the compressed size from the original size: 20 - 5 = 15 MiB, not by adding.

Key Term

compression saves storage

Compressed files are smaller, so they take up less storage space. This means more photos or songs fit on a device, and less storage needs to be bought.

Fill in the Blanks

1. IF compressedSize < originalSize THEN

Hint: Type the comparison operator that is true when the compressed file takes up less space than the original.

2. OUTPUT originalSize - compressedSize

Hint: Type the arithmetic operator that works out how much storage space compression saves.

3. OUTPUT freeSpace DIV compressedSize

Hint: Type the pseudocode operator that gives a whole number of compressed files that fit in the free space.

4. IF compressedSize < originalSize THEN OUTPUT "More files fit" ENDIF

Hint: Type the keyword that starts the block of code run when the condition is true.

5. OUTPUT saved / originalSize * 100

Hint: Type the operator that divides the space saved by the original size to give the percentage of storage saved.

Spot the Error

Question 1

A storage = 64

B photo = 4

C compressed = 1

D count = storage // photo

E print(count)

Line D — The number of files that fit is found by dividing the storage by the compressed size (compressed), not the original photo size. It should be count = storage // compressed.

Question 2

A # Compressed files are larger

B song_mb = 6

C small_mb = 3

D print(song_mb - small_mb)

Line A — Compression makes files smaller, which is why they take up less storage space. The comment should say smaller, not larger.

Question 3

A IF compressed > original THEN

B OUTPUT "More files fit"

C ELSE

D OUTPUT "Fewer files fit"

E ENDIF

Line A — More files fit when the compressed size is smaller than the original size. The test should be compressed < original.

Question 4

A photo_mb = 5

B small_mb = photo_mb * 5

C print(small_mb)

Line B — Compressing the photo to one fifth of its size means dividing by 5. Multiplying would make the file bigger. It should be small_mb = photo_mb / 5.

Question 5

A cost = 2

B big = 100

C small = big * 1.4

D print(small * cost)

Line C — A compressed file is smaller than the original, so it must be less than 100. Multiplying by 1.4 makes it bigger. It should be small = big * 0.4, which gives 40.

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