HP 48SX

HP 48 series
Company type	Product line
Industry	Calculator manufacturing
Founded	1990; 36 years ago
Defunct	2003
Fate	Discontinued
Headquarters	United States
Area served	Worldwide
Products	Graphing calculators (HP 48S, 48SX, 48G, 48GX, 48G+)
Owner	Hewlett-Packard

The HP 48 series consists of a range of graphing calculators produced and sold by Hewlett-Packard between 1990 and 2003. This lineup includes the HP 48S, HP 48SX, HP 48G, HP 48GX, and HP 48G+ models. The G variants are upgraded iterations of the S series, while the X suffix designates models that support expansion through dedicated RAM and ROM modules. Specifically, GX versions provide more built-in memory than the G models, whereas G+ versions increase onboard memory without expansion capabilities. The S and SX models share the same internal memory size.

Although bearing a similar name, the hp 48gII released in 2004 is not included in this series; it is instead closely linked to the HP 49g+ calculators.

These devices operate using Reverse Polish Notation (RPN) and are programmable with the RPL. The architecture of the HP 48 influenced later calculators such as the HP 38G, which featured a simpler user interface with infix notation, and the HP 49G, which introduced software improvements. The design lineage also traces back to earlier HP models like the HP-18C and the HP-28 series.

Models / Availability

The HP 48SX made its debut on March 6, 1990.

Availability timeline:

HP 48SX: 1990 to 1993
HP 48S: 1991 to 1993
HP 48GX (F1895A): 1993 to 2003
HP 48GX ASEE edition: Released in 1993 as a special "1893 ASEE Shaping Our World - Century II" version
HP 48G: Available from 1993 through 2003
HP 48G+ (F1630A, F1894A): Sold between 1998 and 2003

Specifications

The HP 48 series is powered by the Saturn microprocessor, a hybrid CPU featuring both 64-bit and 20-bit operations with nibble-oriented data handling and addressing. Its primary registers—A, B, C, D—and temporary registers R0 through R4 are all 64 bits wide; meanwhile, data registers D0 and D1 are sized at 20 bits. External data accesses translate into physical operations on an 8-bit bus. The processor’s address bus spans 20 bits logically, but only 19 bits are accessible externally due to nibble selection constraints.

In both the HP 48S/SX and G/GX lines, the Saturn CPU core is integrated into a complex IC package named after members of the Lewis and Clark Expedition: the S/SX models use the Clarke chip (named for William Clark), while the G/GX models employ the Yorke chip (named after Clark’s servant York). Earlier Saturn ICs were designated Lewis.

General specifications across all models

Processor architecture: Saturn
Display resolution: 131×64 pixels; three different LCD types were introduced over time to enhance clarity
Connectivity options: Includes a four-pin RS-232 serial port (UART supporting speeds from 1200 to 9600 baud with parity settings) plus an Infrared port (not compliant with IrDA standards)
External data bus width: 8 bits
Maximum addressable memory space: Logical addressing up to 20 bits (512 KB)
Largest register size: 64 bits
Expansion slots on X-series models: Two ports with a 40-pin interface

HP 48S / HP 48SX Specific Details

Processor clock speed: Runs at 2 MHz
Memory clock speed: Also operates at 2 MHz
CPU codename: Clarke (Saturn HP1LT8 core)
Supported communication protocol(s): Kermit
Internal ROM capacity: 256 KB
Internal RAM capacity: 32 KB
Maximum expandable memory per card (only for SX): Up to128 KB
Available ROM firmware versions: A, B, C, D, E, F, J
Features orange and blue shift keys for extended functionality

HP 48G / HP 48GX / HP 48G+ Specifics

Processor clock speed: ranges between 3.68 and 4 MHz
- As explained by HP engineer Dave Arnett, CPUs operating around 3.93–3.94 MHz were initially designated for expandable models (GX), whereas slightly slower CPUs were allocated to the non-expandable versions (G). Subsequent improvements in manufacturing yields enabled nearly 4 MHz CPUs to be used across all variants. Frequency variations due to temperature are negligible.
Memory clock speed: 2 MHz
CPU codename: Yorke (based on the Saturn architecture)
Supported communication protocols: Kermit (protocol) and Xmodem
Integrated ROM capacity: 512 KB
Built-in RAM size: 32 KB for the 48G, and 128 KB for the 48G+ and 48GX models
Maximum memory expansion through ports: up to 128 KB on port 1, and up to 4 MB on port 2 (with bank switching allowing access to 128 KB segments)
Available ROM versions include: K, L, M, P, and R
Shift keys are color-coded in purple and blue-green, which may pose visibility challenges for users with red-green color blindness

Programming

The HP 48 series employs a stack-oriented programming language known as RPL, which merges principles from both Reverse Polish notation and Lisp. RPL extends traditional stack-based programming by supporting lists and functions capable of handling unevaluated code as inputs or outputs.

There exist two flavors of RPL: User RPL and System RPL. User RPL can be programmed directly on the calculator, featuring command restrictions that prevent system crashes but result in slower execution speeds. In contrast, System RPL requires an external compiler, granting access to more low-level operations at the expense of potential system instability if misused.

Moreover, assembly programming for the HP Saturn processor is feasible through on-device utilities such as Jazz or via external compilers made available by HP or third-party developers.

Emulators

Emu48 – Windows platform
Alcuin – Commodore Amiga
X48 – Mac OS X and POSIX-compliant systems (Unix/Linux)
i48 – HP48GX emulator for iOS, derived from X48
m48 – iPhone emulator for HP48 based on Emu48
Droid48 – Android HP48G emulator built upon X48
droid48sx – Android HP48SX emulator based on Droid48
HP48 emulator and decompiler – Compatible with Unix/Linux or Windows (via Cygwin), developed by Paul Courbis

In Popular Culture

An HP 48 calculator is featured in the 2012 motion picture The Amazing Spider-Man as well as its follow-up film.

External links