Types of
Data Transmission

Serial · Parallel · Simplex · Half-Duplex · Full-Duplex

CSZoneCambridge IGCSE Computer Science 0478

Serial vs Parallel Transmission

How Bits Travel

Serial: bits sent one at a time along a single wire. Slower but reliable over long distances — no skew problems. Used by USB, Ethernet, Wi-Fi.

Parallel: multiple bits sent simultaneously along multiple wires. Faster over short distances but bits can arrive out of sync (skew). Used internally in computers (CPU buses).

Over long distances, parallel transmissions suffer from interference — serial is preferred

Direction of Transmission

Simplex, Half-Duplex & Full-Duplex

Simplex: one direction only. e.g. TV broadcast, keyboard → computer

Half-duplex: both directions but not at the same time. e.g. walkie-talkie, older Wi-Fi

Full-duplex: both directions simultaneously. e.g. telephone, modern Ethernet

Bandwidth & Latency

Speed of Data Transfer

Bandwidth: maximum amount of data that can be transmitted per second (bps, Kbps, Mbps, Gbps)

Latency: delay between sending and receiving data — measured in milliseconds

High bandwidth with low latency = fast, responsive network connections

Baud rate: number of signal changes per second (not the same as bits per second)

Exam Practice

Have a go at this question

Cambridge IGCSE 0478 style

State one advantage and one disadvantage of parallel data transmission compared to serial data transmission.

2 marks

Advantage: more bits sent simultaneously so faster data transfer [1]. Disadvantage: bits can arrive at different times (skew/interference) causing errors, especially over long distances [1].

Key Takeaways

What to Remember

Serial: 1 bit at a time, reliable long-distance; Parallel: multiple bits at once, short-distance only

Simplex: one-way; Half-duplex: both ways not simultaneously; Full-duplex: both ways at once

Bandwidth: data capacity per second; Latency: delay in transmission

USB and Ethernet use serial; internal CPU buses use parallel