← IGCSE Computer Science Paper 1

Advantages and disadvantages of parallel transmission

Sends several bits at once on many wires. Fast over short distances, but needs more wires (higher cost) and is unreliable over long distances because of interference between wires.

Part of: IGCSE Computer Science 0478 — 2.1 Data Transmission Types and Methods — Module 25

Understanding Advantages and disadvantages of parallel transmission in IGCSE Computer Science Paper 1

What it does: Short distances keep interference low, so parallel works well for internal links like the bus between the CPU and memory. Parallel transmission needs one wire for each bit sent at the same time. More wires means higher cost. Wires carrying signals side by side cause interference (crosstalk). Over long distances this can corrupt the data.

Common mistakes: Parallel transmission sends several bits at once, so over a short distance it is fast. The line should be speed ← "FAST". Parallel needs many wires, so the cable and connectors cost more. The line should be cost ← "HIGHER".

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Learning
Duo
Parallel transmission over a short distance, such as inside a computer, is...
Slow, because only one bit is sent at a timeFast, because several bits are sent at once
Matches
"Parallel transmission is best for sending data over long distances."
↓
Parallel is unreliable over long distances because of interference between wires. It is best for short distances.
Applying
Meanings
Term
parallel transmission
Meaning
Sends several bits at once on many wires. Fast over short distances, but needs more wires (higher cost) and is unreliable over long distances because of interference between wires.
Practice
// Parallel transmission
Testing
Gaps
wiresNeeded ←
Check Answer
Spots
3distance ← "SHORT"
4speed ← "SLOW"

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Quick Questions

1. Parallel transmission over a short distance, such as inside a computer, is...
A. Fast, because several bits are sent at once ✓
B. Slow, because only one bit is sent at a time
Parallel transmission uses many wires so several bits travel together in each clock tick. Over short distances this makes it fast.
2. Which is a disadvantage of parallel transmission?
A. It needs more wires, so the cables cost more ✓
B. It needs only one wire, so data is lost
Parallel transmission needs one wire for each bit sent at the same time. More wires means higher cost.
3. Why is parallel transmission unreliable over long distances?
A. The wires run out of bits to send
B. Interference between the wires corrupts the data ✓
Wires carrying signals side by side cause interference (crosstalk). Over long distances this can corrupt the data.
4. Where is parallel transmission best suited?
A. Long cables between cities
B. Short links inside a computer, such as between the CPU and memory ✓
Short links have little interference, so the speed advantage of parallel transmission can be used reliably.
5. Which statement about the cost of parallel transmission is correct?
A. It costs more because it needs more wires ✓
B. It costs less because it needs fewer wires than serial
Parallel transmission needs several wires (one per bit), while serial transmission needs far fewer.

Match the Pairs

8 bits sent at once on 8 wires → Parallel transmission sends several bits per clock tick, so it is fast over a short distance
32 wires in a cable → Parallel transmission needs more wires, so the cable costs more to make
Parallel transmission is suited to very short links, such as inside a computer → Data bus between the CPU and RAM
Over long distances, parallel transmission becomes unreliable because wires interfere with each other → Bits on neighbouring wires interfere, so data arrives corrupted over a 50 m cable
"Parallel transmission is best for sending data over long distances." → Parallel is unreliable over long distances because of interference between wires. It is best for short distances.
"Parallel transmission needs fewer wires than serial, so it is cheaper." → Parallel needs more wires than serial, which makes it more expensive, not cheaper.

Key Term

parallel transmission
Sends several bits at once on many wires. Fast over short distances, but needs more wires (higher cost) and is unreliable over long distances because of interference between wires.

Fill in the Blanks

1. bitsPerTick ← 8 wiresNeeded ← bitsPerTick
Hint: Type the variable name. Parallel transmission needs one wire for each bit sent at once.
2. bitsPerTick ← 8 clockTicks ← 4 bitsSent ← bitsPerTick * clockTicks
Hint: Type the operator that multiplies bits per tick by the number of ticks to show why parallel sends more data.
3. wireCost ← 2 totalCost ← wiresNeeded * wireCost
Hint: Type the variable holding the price of one wire. More wires means a higher total cost.
4. IF distance = "long" THEN OUTPUT "Interference: unreliable" ENDIF
Hint: Type the keyword that starts a conditional check on the link distance.
5. IF link = "inside computer" THEN OUTPUT "Use parallel" ENDIF
Hint: Type the pseudocode keyword that displays a message, here a recommendation for a short internal link.

Spot the Error

Question 1
A mode ← "PARALLEL"
B bitsPerTick ← 8
C distance ← "SHORT"
D speed ← "SLOW"
Line D — Parallel transmission sends several bits at once, so over a short distance it is fast. The line should be speed ← "FAST".
Question 2
A link ← "PARALLEL"
B wires ← 8
C cost ← "LOWER"
Line C — Parallel needs many wires, so the cable and connectors cost more. The line should be cost ← "HIGHER".
Question 3
A IF link = "SERIAL" THEN
B wires ← 8
C ENDIF
Line A — Using 8 wires is a feature of parallel transmission, not serial (which uses one wire for data). The test should be IF link = "PARALLEL" THEN.
Question 4
A distance ← 0.1
B IF distance > 1 THEN
C mode ← "PARALLEL"
D ENDIF
Line B — Parallel is best over short distances, so the test should be distance < 1. Using > would choose parallel for long distances, where it is unreliable.
Question 5
A distance ← 50
B IF distance > 10 THEN
C mode ← "SERIAL"
D reason ← "LOW COST"
E ENDIF
Line D — Parallel is avoided over long distances because interference between the wires makes it unreliable. The line should be reason ← "INTERFERENCE".

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