What length is the cable, and what material is it made of?

The lock comes with a 6 ft (1.8 m) carbon steel cable that resists cutting attempts.

Will the slim Nano lock head interfere with my laptop’s I/O ports or lift the device off its surface?

No. The slim nano lock head design is made so it won't interfere with I/O ports or raise the device off its surface.

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Kensington Slim NanoSaver 2.0 Keyed Laptop Lock - Master Key on Demand - 6 ft Cable - K63388WW

Slim nano lock head design won't interfere with I/O ports or raise the device off its surface.
Each Kensington lock is precision engineered to meet or exceed rigorous industry standards for strength, physical endurance, and mechanical resilience.
Six-foot (1.8m) carbon steel cable resists cutting attempts. Protective sheathing helps keep attachment points such as desks and tables free from scratches.
5mm keying system, common across all of Kensington's latest locks, so there's only one keying system to manage. Smaller key opening helps thwart picking attempts.
Register & Retrieve™, Kensington's online key registration program that allows for quick, secure, and free key replacement if ever lost or stolen.
Five-year limited warranty, so you can rest assured knowing you're covered by Kensington, inventor and a worldwide leader in laptop security locks.
Kensington recognizes that most businesses operate differently and offers custom solutions that allow users to select the ideal level of IT control over their equipment, while helping employees safeguard against theft and avoid downtime due to misplaced keys.