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The left-hand sides of the three notebooks all carry a pair of audio jacks (mic/headphone) and a USB port; the Classmate and Eee add an RJ-45 Ethernet connector and a fan intake — features missing from the wireless-only, passive-cooled OLPC XO. The latter's ear-like antennas cater for 802.11s mesh networking as well as standard 802.11b/g Wi-Fi connectivity (also supported in the Classmate and Eee).
The connector for the XO's 12V AC adapter is also on the left-hand side: the notebook is designed to work with off-grid power sources such as solar panels and car batteries; a human-powered 'yo-yo' pull-cord generator has also been designed, although this is not yet widely available.
Another unusual feature of the XO is its microphone input, which can also be used to measure voltage and resistance, allowing sensors to be plugged in and their output recorded by the included Measure application (or 'activity' in OLPC's terminology).