This device is a wax tablet dating from ancient Roman times, and found underneath the city of Barcelona. Just about palm sized. Easy to tuck into a purse or pocket, folds of your toga, or whatever. When folded, it would be just about the same size as the original Palm Pilot.
Seeing this on a recent trip to Barcelona reminded me that many of our needs are old and unchanging. We've wanted ways to record information and take it with us. The difference now is that we have found more and better ways to do that. The wax tablet was an improvement over papyrus because it was small and reusable. Papyrus was probably invented to be an improvement over stone carving. The fundamental need to record things has clearly been with us for thousands of years.