Parallel transmission

Parallel transmission is when we have multiple wires which we send data down, all at the same time.

For example, if we have 8 wires, we can send 8 different bits at the same time.

Advantages of parallel transmission

Compared to serial transmission, parallel transmission can be faster, because it can send multiple bits at the same time. However, this isn’t always the case, as you’ll see.

Disadvantages of parallel transmission

The main disadvantages of parallel transmission compared to serial transmission are that:

• It’s more expensive to implement as it requires multiple wires (and connectors, etc).
• It’s less reliable as there is more chance of interference between the wires (called crosstalk).
• It can only be used over short distances as the signal is more likely to degrade over multiple wires.
• It can be slower than serial transmission, as the wires can only be run at a lower frequency without interference.
• There can be skew issues, where the bits can get out of sync, because they are sent at the same time, but can take different amounts of time to arrive at the destination.
• It’s harder to implement error detection and correction, as the bits are sent at the same time, so it’s harder to detect if a bit is missing or corrupted.
• (Among lots of other disadvantages)

Examples of parallel transmission

The main examples are the internal data buses in a computer.

For example, modern computers are 64 bit, which means that each data bus can carry 64 bits at a time.

That means that there are actually 64 tiny wires on the motherboard, which can carry signals of 64 bits (or 8 bytes) at a time from/to the CPU and the different components.

Outside of internal buses, parallel transmission is almost never used in the modern world because it’s just not worth the many disadvantages. You’ll see it a lot in older connections, because back then they thought that parallel was the future… turns out it wasn’t :)