Continuous memory

The term continuous memory was used by HP calculators to indicate that the calculator can preserve most or (later) all of the contents of user memory (in RAM) at all times. Since its introduction, this feature has slowly evolved to finally include the contents of nearly all calculator memory, including system/scratch RAM, flags, and calculator state data.

Before the introduction of the HP-25C (the first model with this feature) in 1976, all calculator random access memory (RAM) was volatile, i.e. its contents (data in storage registers and program memory (if any)) was lost when the calculator was turned off. The three models - HP-25C, HP-29C, and HP-19C - had the words "Continuous Memory" printed in white script on the bottom margin of their faceplates. After the novelty (and HP's exclusivity) of continuous memory faded, the printing of this phrase on subsequent calculator models with this feature was discontinued. For approximately 9 years (1979-1987), subsequent models with this feature simply had designations in which the letter "C" followed the model number, like the [HP-34C] and the HP-10C series.