Cambridge O Level Computer Science · Syllabus 2210 · Data Transmission
Serial Transmission
What is Serial Transmission?
Serial transmission is a method of data transmission in which bits are sent one after another along a single data line, one bit at a time.
This definition is part of the Data Transmission chapter in Cambridge O Level Computer Science.
Serial Transmission in context
Serial and parallel answer one question: how many bits travel at once, and on how many data lines? In serial transmission, bits are sent one after another along a single data line. In parallel transmission, several bits are sent at the same time, each along its own data line. Neither is simply “better”: parallel moves more bits per unit of time over a short link, but over distance the separate lines lose their alignment and interfere with one another, which is why long links are almost always serial.
USB stands for universal serial bus. It is an interface — an agreed standard for connecting a device to a computer and transmitting data between them. It uses serial transmission: the bits travel one after another along the connection. Because both ends follow the same agreed communication standard, a device made by one manufacturer can be plugged into a computer made by another and the two can exchange data. The name describes the design: universal (one widely supported standard for many kinds of device), serial (bits one after another) and bus (a shared connection system carrying data and power between the computer and the connected devices).
Examiner tips on Serial Transmission
- The sentence shape that always works for a scenario answer: “Use [method], because the scenario says [feature of the scenario], and [method] [property that matches that feature].” For example: “Use serial transmission, because the cable runs 40 metres to the sensor, and serial sends bits one after another on a single line, so there is no skew between separate wires over that distance.” The middle two clauses — the feature of the scenario, and the property that matches it — carry the substance of the answer.
Questions students ask about Serial Transmission
What is the difference between serial and parallel transmission?
In serial transmission, bits are sent one after another along a single data line. In parallel transmission, several bits are sent at the same time, each along its own separate data line. Parallel can move more bits per unit of time over a short link, but over a longer distance the separate lines lose their timing alignment and interfere with one another, which is why long-distance links, such as USB, almost always use serial transmission instead.