HP 48 series

HP 48
Company type	Product line
Industry	Electronics, Calculators
Predecessor	HP-18C, HP-28 series
Founded	1990
Defunct	2003
Headquarters	Palo Alto, United States
Products	Graphing calculators (models HP 48S, SX, G, GX, G+)
Parent	Hewlett-Packard

The HP 48 line of graphing calculators was produced and sold by Hewlett-Packard between 1990 and 2003. This series comprises models like the HP 48S, SX, G, GX, and G+. The G versions represent upgraded iterations of the S models, whereas those with an X suffix accommodate memory expansion through RAM and ROM cards; among these, the GX models possess more internal memory compared to the G variants. The G+ editions solely enhance onboard memory capacity. Both the SX and S versions maintain identical internal memory sizes.

Although bearing a similar name, the hp 48gII released in 2004 does not belong to this series but is closely linked to the HP 49g+.

These calculators operate using Reverse Polish Notation (RPN) alongside HP’s exclusive RPL. The hardware design introduced with the HP 48 served as a blueprint for later models such as the HP 38G, which offers a more streamlined interface and infix notation input, as well as the HP 49G, which includes software advancements. The overall design lineage traces back to earlier HP calculators like the HP-18C and the HP-28 series.

Models / Availability

The HP 48SX was first released on March 6, 1990.

Availability timeline:

48SX: available from 1990 until 1993
48S: produced between 1991 and 1993
48GX (F1895A): sold from 1993 through 2003
48GX ASEE: a special edition launched in 1993 ("1893 ASEE 1993 Shaping our world - Century II")
48G: on market from 1993 to 2003
48G+ (F1630A, F1894A): manufactured from 1998 until 2003

Specifications

The HP 48 series incorporates the Saturn microprocessor, a hybrid CPU combining 64-bit and 20-bit architecture that processes data and addresses in nibbles. The primary registers—A, B, C, D—and temporary registers R0 through R4 are all 64 bits wide, while data registers D0 and D1 operate at 20 bits. External data retrieval transparently converts to physical fetches of 8 bits. Although the processor's address bus supports up to 20 bits, only 19 bits are externally accessible due to nibble selection constraints.

Both HP 48S/SX and G/GX models embed the Saturn core within complex integrated circuits named after figures from the Lewis and Clark Expedition: Clarke for S/SX models (named after William Clark) and Yorke for G/GX units (named after Clark’s servant Yorke). Earlier series utilized Lewis ICs named after Meriwether Lewis.

Common features across all models

CPU type: Saturn architecture
Display resolution: 131×64 pixels with three different LCD versions enhancing contrast and readability
Connectivity options: includes a 4-pin RS-232 serial interface (UART supporting baud rates from 1200 to 9600 with parity settings) plus an infrared port (non-IrDA, pulse-based)
External data bus width: 8 bits
Maximum nibble-cell address width: 20 bits
Logical addressing capacity: up to 512 KB
Largest register size: up to 64 bits for both working and temporary registers
Expansion slots on X models: two available
Expansion card connector pins: forty

Details specific to HP 48S/HP 48SX

Processor clock speed: runs at 2 MHz
Memory clock speed: also at 2 MHz
CPU codename: Clarke (Saturn HP 1LT8 core)
Supported communication protocol(s): Kermit
Internal ROM size: 256 KB
Internal RAM size: 32 KB
Maximum expandable memory per card (exclusive to the SX): up to 128 KB
Available ROM firmware versions: A, B, C, D, E, F, J
Shift keys colored orange and blue

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

Processor clock speed ranges from 3.68 to 4 MHz
- According to engineer Dave Arnett, CPUs operating around 3.93–3.94 MHz were originally allocated to expandable models (GX), while those with slightly reduced frequencies were designated for non-expandable (G) versions; advancements in manufacturing later enabled nearly 4 MHz processors across all units. Frequency variations due to temperature are negligible.
Memory clock speed: 2 MHz
Processor codename: Yorke (based on the Saturn architecture)
Supported communication protocols include Kermit (protocol) and Xmodem
Internal ROM capacity: 512 KB
Internal RAM size: 32 KB for the 48G, and 128 KB for the 48G+ and 48GX models
Expansion memory support: up to 128 KB on port 1, and up to 4 MB on port 2 (with bank switching allowing access to 128 KB segments)
ROM firmware versions identified as K, L, M, P, and R
Design consideration: The purple and blue-green shift keys may pose challenges for individuals with red-green color vision deficiency

Programming

The HP 48 series utilizes a stack-oriented programming language known as RPL, which blends elements from Reverse Polish notation and the Lisp paradigm. RPL facilitates the handling of unevaluated code fragments as function inputs or produces them by leaving code on the stack.

There are two variants of RPL: User RPL and System RPL. User RPL can be programmed directly on the calculator, offering a safer environment with commands designed to prevent crashes, albeit at slower execution speeds. Conversely, System RPL requires an external compiler and grants access to low-level operations, enabling faster performance but at the expense of increased risk of system instability if improperly coded.

Furthermore, assembly programming for the HP Saturn processor is supported through on-device tools such as Jazz or via external Hewlett-Packard utilities like SASM.

Emulators

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

In Popular Culture

The HP 48 calculator makes an appearance in the films The Amazing Spider-Man and its follow-up installment.

External links