Thunderbolt is a connection that allows you to attach external peripherals to a computer, and can carry both data and display signals. Using a single port you can connect up to six devices through a hub or daisy chain configuration.
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16. RJ45 ports
RJ-45 ports are used for LAN (Local Area Network) connections. With more ports you can achieve increased bandwidth across a LAN, or connect to multiple networks. It also has the added benefit of not losing connection to the network if one fails.
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17. PS/2 ports
PS/2 ports are used to connect mice and keyboards. Although they have been replaced by USB, they are still useful in corporate environments where USB ports are disabled for security reasons.
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18. audio connectors
More connectors means that more audio devices such as speakers or microphones can be connected.