← IGCSE Computer Science Paper 1

Comparing serial and parallel transmission

Serial sends 1 bit at a time down one wire: cheaper, reliable, better over long distance. Parallel sends many bits at once down several wires: faster over short distances only.

Part of: IGCSE Computer Science 0478 — 2.1 Data Transmission Types and Methods — Module 27, WA Computer Science ATAR Year 11 — Network Communications — Module 19

Understanding Comparing serial and parallel transmission in IGCSE Computer Science Paper 1

What it does: Serial avoids data skew, so it stays reliable over long distances. Parallel is not suited to them. Parallel sends several bits per clock tick, which gives higher speed when the wires are short and skew is not a problem. The second option describes parallel. Serial trades some speed for reliability and a longer range. Serial transmission uses one wire and sends one bit at a time, which keeps cabling simple and cheap. The number of wires is the reverse of what the broken statement claims: serial has fewer wires, so it costs less.

Common mistakes: Serial is the better choice over longer distances because parallel suffers from data skew. Line 3 should read 'longer distance: serial'. Parallel transmission uses several wires, one per bit, so it does not use 1 wire. It should be 'parallel: wires = 8'.

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This module's key terms are also in a printable crossword (Modules 121–130) and word search (Modules 121–141).

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Learning
Duo
Which method sends several bits at the same time down several wires?
Serial transmissionParallel transmission
Matches
Parallel is best for sending data over long distances because it uses more wires
↓
Parallel is not suited to long distances. Data skew makes bits arrive at different times and the data becomes unreliable. Serial is better for long distances.
Applying
Meanings
Term
serial vs parallel
Meaning
Serial sends 1 bit at a time down one wire: cheaper, reliable, better over long distance. Parallel sends many bits at once down several wires: faster over short distances only.
Practice
Serial: 1 bit at a time, 1 wire
Testing
Gaps
serial: bits sent at once =
Check Answer
Spots
2parallel: bits at once = 8
3longer distance: parallel

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Quick Questions

1. Which method sends several bits at the same time down several wires?
A. Parallel transmission ✓
B. Serial transmission
Parallel uses multiple wires so many bits travel at once. Serial sends only 1 bit at a time down a single wire.
2. Which method is better for sending data over a long distance?
A. Parallel transmission
B. Serial transmission ✓
Serial is more reliable over long distances because there is no data skew. Parallel is only suitable over short distances.
3. Which statement is correct?
A. Parallel is faster than serial over a long distance
B. Parallel is faster than serial over a short distance ✓
Parallel sends more bits per clock pulse, so it is faster over short distances. Over long distances, skew makes it unreliable.
4. Why is parallel transmission unreliable over long distances?
A. Bits can arrive out of sync because of data skew ✓
B. It can only send 1 bit at a time
Data skew happens when bits on different wires arrive at slightly different times. Sending 1 bit at a time describes serial.
5. Which method usually costs less to wire up?
A. Serial, because it needs fewer wires ✓
B. Parallel, because it needs fewer wires
Serial needs only one wire (or a few), so cables and connectors are cheaper. Parallel needs many wires, which costs more.

Match the Pairs

Serial: 1 bit at a time, 1 wire → Serial sends one bit after another down a single wire, so it needs less wiring and costs less.
Parallel: 8 bits at once, 8 wires → Parallel sends several bits at the same time down separate wires, so it is faster but only over short distances.
Over a long distance, serial is the better choice because the bits stay in step and arrive reliably → distance = "long" method = "serial"
Over a very short distance, parallel can be faster because many bits travel at once → distance = "short" method = "parallel"
Parallel is best for sending data over long distances because it uses more wires → Parallel is not suited to long distances. Data skew makes bits arrive at different times and the data becomes unreliable. Serial is better for long distances.
Serial is more expensive than parallel because it needs more wires → Serial uses only one wire, so it needs less wiring and is cheaper. Parallel uses many wires, which costs more.

Key Term

serial vs parallel
Serial sends 1 bit at a time down one wire: cheaper, reliable, better over long distance. Parallel sends many bits at once down several wires: faster over short distances only.

Fill in the Blanks

1. serial: bits sent at once = 1
Hint: Type the number of bits serial transmission sends at one time.
2. parallel: bits sent at once = many
Hint: Type the word describing how many bits parallel sends at once, using several wires.
3. long distance: serial is more reliable
Hint: Type the transmission method that suits long distances.
4. parallel over distance causes data skew
Hint: Type the problem where bits on different wires arrive at slightly different times.
5. short distance, high speed: parallel
Hint: Type the transmission method that is faster but only over short distances.

Spot the Error

Question 1
A serial: bits at once = 1
B parallel: bits at once = 8
C longer distance: parallel
Line C — Serial is the better choice over longer distances because parallel suffers from data skew. Line 3 should read 'longer distance: serial'.
Question 2
A serial: wires = 1
B parallel: wires = 1
C cheaper wiring: serial
Line B — Parallel transmission uses several wires, one per bit, so it does not use 1 wire. It should be 'parallel: wires = 8'.
Question 3
A serial: sends 8 bits at once
B parallel: sends 8 bits at once
C short range: parallel faster
Line A — Serial sends only 1 bit at a time down a single wire. Sending many bits at once is parallel.
Question 4
A distance ← "long"
B IF distance = "long" THEN
C method ← "parallel"
D ENDIF
Line C — Over a long distance parallel suffers from data skew and costs more, so serial should be chosen. Line 3 should be method ← "serial".
Question 5
A Feature | Serial | Parallel
B Bits at once | 1 | many
C Wires | 1 | several
D Cost | higher | lower
E Short range | slower | faster
Line D — The cost values are swapped. Serial needs only one wire so it is cheaper, while parallel needs several wires so it costs more.

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