(my own hp48gx as December 2012, I bought it around 1995)
HP48 is a scientific calculator with ability to draw graph. The product was launched in 1990 and was discontinued in 2003. Because of its popularity, it has been "emulated" in software. The original calculator uses 64 bit CPU with 4-bit data bus to communicate with program ROM. The details of its Saturn processor can be found here (from http://grack.com/writings/hp48/GuidetotheSaturnProcessor.html). The history of this series of calculator can be read from wiki. The HP48GX runs its processor at 4 MHz.
Software emulation performs the function of Saturn processor, i.e. the
emulator executes Saturn binary code. The program for the real calculator
(stored in its ROM) is used in the emulator. So, all the effort of
producing this complex piece of software (this is the advanced scientific
calculator) is preserved and it continue to work in the new environment.
You can download the emulator (emu48) from
http://hp.giesselink.com/emu48.htm . A local copy of the emulator
including the ROM version R can be found here.
(It works on my Windows XP, 7 and 8).
The later models, 49g+ and 50g use different processor, an ARMv4T running at 75MHz. To save the software effort, they also execute the program in emulation mode (where ARM CPU runs an emulation of Saturn processor). This is a fine example of how a digital technology can have a long life, by evolving through the generation of new technology (in this case, a new processor).
last update 3 Dec 2012