Apple prototype collector Giulio Zompetti has shared photos of the first iPad with two 30-pin connectors.
The first connector, as in the final version of the device, is located on the bottom edge, and the second is located on the left side.
It is assumed that the connector was used when testing the device and supported parallel charging. It could also have been docked for tablet use in both landscape and portrait orientations.
Back in 2012, the first iPad was listed on eBay. It also had two connectors. Then it was reported that Steve Jobs abandoned the second connector almost before the launch of the production of tablets.
In current generations, there is a second connector: Smart Connector is used to connect Smart Keyboard and Magic Keyboard. The Smart Connector can be used for other accessories as well, but there are very few of them.