Today I stumbled across a description of an HP 9100 prototype on the web site of The National Museum of American History. The prototype already looks quite similar to the final calculator. The keys are mostly the same, however, the keyboard layout differs slightly. It looks like the prototype has no magnetic card reader. Unfortunately, there is no picture showing the inside. According to the museum, it was a gift of the Hewlett Packard company. I wonder if it’s still working?