--- title: HP 48GX description: HP's RPL graphing calculator of 1993 to 2003, its history, what makes it special and how saturnus runs it. section: models model: 48gx --- The HP 48GX is a graphing calculator that Hewlett-Packard sold from 1993 to 2003. It took the HP 48SX of 1990, made it easier to learn with input forms and menus to choose from, and added four times the memory, the Equation Library and a card slot for up to 4 MB. ![HP 48GX](../img/48gx-640.webp) The 48GX as saturnus draws it, plotting a sine curve. ## At a glance | | | |---|---| | Released | June 1993, at $350 | | Discontinued | May 2003 | | Processor | Saturn core in HP's Yorke chip, 4 MHz | | Memory | 128 KB RAM, 512 KB ROM | | Card slots | Two: slot 1 up to 128 KB, slot 2 up to 4 MB | | Display | 131 × 64 pixels, 8 lines of 22 characters | | Keyboard | 49 keys, with a purple and a green shift key | | Input and output | Serial port (1200 to 9600 baud), two-way infrared, beeper | | Power | Three AAA cells | | Size and weight | 180 × 81 × 25 mm, 264 g | | ROM revisions | K, L, M, P and R | ## History ### From the 48SX to the 48G series The HP 48SX came out in 1990 and was becoming a standard among engineering students and engineers. Teachers told HP it was too hard to use and too expensive for the classroom. At a meeting of the American Mathematical Society in January 1992, HP decided it needed a new calculator for schools by the 1993 back-to-school season. A committee of six mathematics professors advised on the design. The first design goal was to make the calculator easy to learn. Users had said the 48SX's manual and its many operations were too much for beginners, while experienced users forgot how to use the parts they rarely needed. The answer was input forms: each application asks for its values in a form to fill in, with choose lists for the options. The second goal was graphing that went beyond the competition, the third more advanced mathematics. HP's own article on the calculator, in the Hewlett-Packard Journal of August 1994, tells this story. It was written by five of the developers. ### What changed | | 48SX | 48G | 48GX | |---|---|---|---| | RAM | 32 KB | 32 KB | 128 KB | | ROM | 256 KB | 512 KB | 512 KB | | Clock | 2 MHz | 4 MHz | 4 MHz | | Card slots | 2 | none | 2 | | Plot types | 8 | 15 | 15 | The new processor runs at twice the clock, but programs run only about 40% faster: the upper half of the ROM and the large cards are reached through bank switching, and the bus is still 4 bits wide. HP kept the 48SX's functions and much of its code, but many programs written in assembly language or System RPL no longer ran, especially those that wrote to the display memory directly. The 48G was the cheaper model, priced to compete with other graphing calculators in high schools. The 48GX, with more memory and the card slots, was meant for college students. Both run the same ROM; the calculator tells which model it is by the size of its RAM. When the G series came out, HP ran a trade-in program for 48S and 48SX owners. ### ROM revisions The first 48G series ROM, revision K, had bugs with the card ports and shipped only in the 48G. Revision L fixed them. Revisions M and P followed, and R was the last. The HP 48 FAQ lists the bugs of each revision; in early 1994 HP offered upgrades for buggy 48GXs. Revision L is also in the 2,000 48GXs sold at the ASEE conference in 1993 for $90 each. To see a calculator's revision, type `VERSION`: the command is in no menu. ### Prices and what came after The price came down over the years: $265 in 1995, $179.95 by mid-1999 and $149.99 in early 2003. In March 1998 HP added the 48G+, a 48G with 128 KB of RAM but still no card slots. All 48G+ calculators have revision R. On 21 May 1999, in Paris, HP announced the HP 49G: the same 4 MHz Saturn, 512 KB of RAM and 2 MB of flash memory, so its ROM can be updated. The 48GX was discontinued on 30 May 2003. The HP 48gII of 2004 has the name but is not a member of the series: it is related to the HP 49g+. ## What makes it special ### RPL The 48GX is programmed in RPL, the language and operating system HP first used in the HP 18C and HP 28C. Bill Wickes of HP wrote in 1991 that the name stands for Reverse Polish Lisp: a play on RPN, and a nod to Forth and Lisp, the languages it comes from. Everything works on a stack of objects: numbers, lists, programs, matrices, unit objects, graphics. The G series added automatic list processing: almost every command now takes a list and works on each element. ``` { 1 2 3 } SQ gives { 1 4 9 } { 2 4 } 10 / gives { .2 .4 } ``` ### Built-in applications - The Equation Library: more than 300 equations in 15 subjects, with more than 100 problem titles, and a library of physical constants. On the 48SX, much of this was a plug-in card. - Units: a catalog of 147 units that numbers carry through calculations. - Plots: the 48SX's eight plot types and seven new ones, among them differential equations, slope fields, wireframe and parametric surface plots. - Solvers for differential equations, polynomial roots and financial problems; Fourier transforms; matrices and linear algebra. The Equation Library caused trouble at exams. The HP 48 FAQ reports that at first only the 48S and 48SX were allowed in the AP Chemistry and AP Physics exams in the US, because the G series had the equations built in. ### Memory cards Slot 1 takes a card of up to 128 KB, which can be merged with the main memory, for up to 256 KB. Slot 2 takes cards of up to 4 MB that the calculator divides into 128 KB ports, numbered from port 2. These ports cannot be merged, and some programs written in machine language do not run from them. The Emu48 manual notes a quirk: with a full 4 MB card the calculator reports "Invalid Card Data" and port 33 cannot be reached. [Memory](saturn/memory.md) explains why. ### Serial and infrared The serial port speaks Kermit, as on the 48SX, and now also XModem. The infrared port talks to another HP 48 and prints to HP's infrared printer. Two calculators must be no more than 2 inches (5 cm) apart, while the printer works at 18 inches (45 cm). The Museum of HP Calculators says HP limited the receiving range because teachers worried about messages passed invisibly in class. The HP 48 FAQ gives two stories: that one, from a remark by Bill Wickes, and battery life, since the receiver draws power the whole time it listens. In the US, the ACT test allowed calculators with infrared from 1996 only with the port covered by opaque tape. ### Hidden things Type `RULES` and the calculator shows a crossword of the first names of its design team. All five authors of the HP Journal article are in it. One word is ALCUIN, the 48G's code name during development: Alcuin was the teacher of Charlemagne, and Charlemagne had been the code name of the 48SX. The game Minehunt is in the Equation Library's UTILS menu: cross an 8 × 16 field from the top left to the bottom right without stepping on a hidden mine. On the 48SX it came on the Equation Library card. ## In saturnus saturnus runs the 48GX with ROM revision R: - Its screens were checked against those of the saturnng emulator, and satx's Kermit tests pass on it. - Programs take as long as on the real calculator, within a few percent. For long ones, switch to 2×, 4× or Max. - The memory view shows variables, directories, the stack and the flags, read live from the calculator's RAM. Variables open in an RPL editor, and a program pasted into the app is typed into the command line key by key. - Files moves variables between your computer and the emulated 48GX, or a real HP 48 on a serial cable (in Chrome or Edge on a computer). - The command-line saturnus also takes RAM card files for both slots, up to 4 MB in slot 2. The [command reference](commands.md#48gx) lists the 48GX's 517 commands with their stack effects, and examples for 431 of them, run in saturnus. [Open the HP 48GX in saturnus](../app/#/calculator/48gx) ## Sources - [HP 48G Series User's Guide](https://literature.hpcalc.org/community/hp48g-ug-en.pdf): units (10-1), the Equation Library, the constants and Minehunt (25-1, 25-11, 25-14), infrared distances (27-1), printing. - [Hewlett-Packard Journal, August 1994](https://www.hparchive.com/Journals/HPJ-1994-08.pdf): "An Advanced Scientific Graphing Calculator" by Diana K. Byrne, Charles M. Patton, David Arnett, Ted W. Beers and Paul J. McClellan: the design story, the plot types, RAM and ROM, the 49 keys, RPL's origin, the processor. - [HP 48 FAQ 4.62](https://www.hpcalc.org/hp48/docs/faq/48faq.html), edited by André Schoorl: the differences from the 48SX and the speed, the ROM revisions and their bugs, the ASEE calculators, the 48G+ and the 49G, `RULES` and the code names, Minehunt, cards and ports, the infrared range, exams, list processing. - [Finseth's HP calculator data: HP 48GX](https://www.finseth.com/hpdata/hp48gx.php): dates and prices, display, size, weight, power, the Yorke chip. - [Museum of HP Calculators: HP-48S/SX](https://www.hpmuseum.org/hp48s.htm): the 48SX and its years, why the infrared range is short. - [Wikipedia: HP 48 series](https://en.wikipedia.org/wiki/HP_48_series): the models and their years, the HP 48gII. - [William C. Wickes, what RPL stands for (1991)](https://www.hpcalc.org/hp48/docs/programming/rpl.txt): the name RPL. - [Christoph Gießelink, Emu48](https://hp.giesselink.com/emu48.htm): the Emu48 manual on the 4 MB card bug.