Cambridge A-Level Computer Science (9618) · lesson 6 of 15 · 25 min
Bandwidth, Latency, and Throughput
Throughput is always less than bandwidth due to protocol overhead, collisions, retransmissions, and network congestion.
Serial vs Parallel Transmission
Paradoxically, modern high-speed interfaces (USB 3, PCIe, SATA) are serial despite seeming slower — at high frequencies, parallel transmission suffers from skew (bits arriving at slightly different times), making serial more reliable at GHz speeds.
Synchronous vs Asynchronous Transmission
What is the difference between bandwidth and throughput?
- They are the same
- Bandwidth is theoretical maximum; throughput is actual achieved rate
- Throughput is always higher than bandwidth
- Bandwidth measures latency
Answer: Bandwidth is theoretical maximum; throughput is actual achieved rate
Bandwidth is the channel capacity; throughput is what is actually achieved after overhead and losses.
Why is parallel transmission not used for long-distance high-speed links?
- It is too expensive
- Skew causes bits to arrive at different times at high frequencies
- It requires more power
- It cannot carry digital signals
Answer: Skew causes bits to arrive at different times at high frequencies
At high frequencies, parallel wires experience skew — bits arrive out of sync, causing errors.
Asynchronous transmission uses start and stop bits to:
- Encrypt data
- Synchronise sender and receiver without a shared clock
- Increase bandwidth
- Detect errors
- Answer: 1
Start/stop bits frame each character so the receiver knows when data begins and ends.
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