How many bytes is the Preamble in an Ethernet header, and what is its purpose?

The Preamble in an Ethernet header is 7 bytes long. Its primary purpose is synchronization, which means it helps the receiving devices prepare for the incoming data frame. Specifically, the Preamble consists of alternating 1s and 0s, which allows the receiving equipment to establish timing for accurate data reception. By ensuring that both the sending and receiving devices are synchronized, it minimizes errors and improves the reliability of data transmission.

Given that synchronization is crucial for proper frame detection, this function of the Preamble is essential in Ethernet communications. The other options do not accurately reflect the Preamble's length or purpose, as they refer to incorrect byte sizes or functions that pertain to other components of the Ethernet frame.