How many bytes compose the 'Preamble' in an Ethernet header?

The Preamble in an Ethernet header is composed of 7 bytes. This component serves a critical role in the Ethernet frame structure. Specifically, the Preamble consists of a series of alternating 1s and 0s (10101010) that helps synchronize the recipient's clock with the sender's clock. This synchronization is crucial because it allows the receiving device to accurately read the incoming bits of the data frame.

The Preamble is followed by the Start Frame Delimiter (SFD), which is 1 byte long, marking the actual beginning of the frame. Together, the Preamble and SFD help ensure that the data transmission is reliable and that devices on the network can effectively communicate without misinterpreting the incoming signal.

Other options are incorrect because they do not accurately reflect the standard Ethernet frame structure as defined in the IEEE 802.3 specification for Ethernet frames. Understanding the precise length of the Preamble is essential for networking professionals, as it forms the foundational aspect of data communication.