← IGCSE Computer Science Paper 1

Sound file size in the unit asked

Divide the sound size in bits by 8 to get bytes, then by 1024 to get KiB. Divide by 1024 again to get MiB. Stop at the unit the question asks for.

Part of: IGCSE Computer Science 0478 — 1.3 Data Storage and Compression — Module 27

Understanding Sound file size in the unit asked in IGCSE Computer Science Paper 1

What it does: The expression shows the two steps in order: bits to bytes (/ 8), then bytes to KiB (/ 1024). Divide bits by 8 to get bytes: 65,536 ÷ 8 = 8,192. Multiplying by 8 goes the wrong way. Bytes to KiB means dividing by 1024: 16,384 ÷ 1024 = 16. Dividing by 8 again would be a mistake, because the data is already in bytes. 3,145,728 ÷ 1024 = 3,072 KiB, then ÷ 1024 = 3 MiB. 3,072 is the answer in KiB, not MiB. Stop at the unit the question asks for. One divide by 1024 gives KiB, and a second one would give MiB.

Common mistakes: Storage units step up by 1024, not 1000. To go from bytes to KiB you divide by 1024, so the line should be KiB = bytes / 1024. There are 8 bits in a byte, so going from bits to bytes means dividing by 8, not multiplying. It should be bytes = bits / 8.

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Learning
Duo
A sound file is 65,536 bits. What is its size in bytes?
524,288 bytes8,192 bytes
Matches
KiB = bits / 8 / 1000
↓
Divides by 1000 instead of 1024. Each step up the storage unit ladder uses 1024, so it should be bits / 8 / 1024.
Applying
Meanings
Term
bits / 8 / 1024
Meaning
Divide the sound size in bits by 8 to get bytes, then by 1024 to get KiB. Divide by 1024 again to get MiB. Stop at the unit the question asks for.
Practice
bits ← 44000 * 16 * 60
Testing
Gaps
bytes = bits /
Check Answer
Spots
2bytes = bits / 8
3KiB = bytes / 1000

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Quick Questions

1. A sound file is 65,536 bits. What is its size in bytes?
A. 524,288 bytes
B. 8,192 bytes ✓
Divide bits by 8 to get bytes: 65,536 ÷ 8 = 8,192. Multiplying by 8 goes the wrong way.
2. A sound file is 16,384 bytes. What is its size in KiB?
A. 16 KiB ✓
B. 2,048 KiB
Bytes to KiB means dividing by 1024: 16,384 ÷ 1024 = 16. Dividing by 8 again would be a mistake, because the data is already in bytes.
3. Which working changes a sound size in bits into MiB?
A. bits ÷ 8 ÷ 1024 ÷ 1024 ✓
B. bits ÷ 8 ÷ 1024
Divide by 8 for bytes, by 1024 for KiB, then by 1024 again for MiB. Stopping after one 1024 only gives KiB.
4. A sound is 7,680,000 bits. What is its size in KiB?
A. 7,500 KiB
B. 937.5 KiB ✓
7,680,000 ÷ 8 = 960,000 bytes, then ÷ 1024 = 937.5 KiB. Skipping the divide by 8 gives 7,500, which is wrong.
5. A sound is 3,145,728 bytes. What is its size in MiB?
A. 3 MiB ✓
B. 3,072 MiB
3,145,728 ÷ 1024 = 3,072 KiB, then ÷ 1024 = 3 MiB. 3,072 is the answer in KiB, not MiB.

Match the Pairs

bits / 8 / 1024 → Converts a sound size in bits to KiB: bits to bytes, then bytes to KiB
bits / 8 / 1024 / 1024 → Converts a sound size in bits to MiB: bits to bytes, KiB, then MiB
To give a sound size in KiB, first divide the bits by 8 to get bytes, then divide by 1024 → KiB = bits / 8 / 1024
Worked example: 32 kHz, 16-bit, 4 minutes. Change to Hz and seconds, multiply, then divide by 8 and by 1024 twice for MiB (about 14.65 MiB) → 32000 * 16 * 240 / 8 / 1024 / 1024
KiB = bits / 8 / 1000 → Divides by 1000 instead of 1024. Each step up the storage unit ladder uses 1024, so it should be bits / 8 / 1024.
MiB = bits / 1024 / 1024 → Misses the divide by 8 step, so the bits never become bytes. It should be bits / 8 / 1024 / 1024.

Key Term

bits / 8 / 1024
Divide the sound size in bits by 8 to get bytes, then by 1024 to get KiB. Divide by 1024 again to get MiB. Stop at the unit the question asks for.

Fill in the Blanks

1. bytes = bits / 8
Hint: Type the number you divide by to turn bits into bytes.
2. kib = bytes / 1024
Hint: Type the variable holding the size in bytes, which is divided to reach KiB.
3. mib = kib / 1024
Hint: Type the arithmetic operator used to move up to a larger unit.
4. seconds = 2 * 60 bits = 44100 * 16 * seconds mib = bits / 8 / 1024 / 1024
Hint: Type the number of seconds in one minute.
5. hz = 44 * 1000 bits = hz * 16 * 60 mib = bits / 8 / 1024 / 1024
Hint: Type the number of Hz in one kHz.

Spot the Error

Question 1
A bits = 44100 * 16 * 60
B bytes = bits / 8
C KiB = bytes / 1000
D OUTPUT KiB
Line C — Storage units step up by 1024, not 1000. To go from bytes to KiB you divide by 1024, so the line should be KiB = bytes / 1024.
Question 2
A bits = 8000 * 8 * 10
B bytes = bits * 8
C KiB = bytes / 1024
D print(KiB)
Line B — There are 8 bits in a byte, so going from bits to bytes means dividing by 8, not multiplying. It should be bytes = bits / 8.
Question 3
A bits = 44100 * 16 * 120
B bytes = bits / 8
C KiB = bytes / 1024
D MiB = KiB / 8
E OUTPUT MiB
Line D — The step from KiB to MiB is a division by 1024. Dividing by 8 is only for the bits to bytes step. It should be MiB = KiB / 1024.
Question 4
A rate = 44.1 * 1000
B secs = 3 * 100
C bits = rate * secs * 16
D OUTPUT bits
Line B — There are 60 seconds in a minute, so 3 minutes is 3 * 60 seconds. The line should be secs = 3 * 60.
Question 5
A rate = 8 * 100
B secs = 2 * 60
C bits = rate * secs * 16
D OUTPUT bits
Line A — 1 kHz is 1000 Hz (samples per second), so 8 kHz is 8 * 1000. The line should be rate = 8 * 1000.

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