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Hewlett-Packard handheld RPN estimator

HP-41C series
Computer
HP-41CX with magnetic card reader and thermal printer
Type	Programmable scientific
Introduced	1979
Discontinued	1990
Entry fashion	RPN
Brandish type	LCD fourteen-segment brandish
Programming
Programming language(due south)	RPN fundamental stroke (fully merged, Turing consummate)
Memory register	63 .. 319
Program steps	441 .. 2233
Interfaces
Ports	four vendor specific
Connects to	micro-cassette via: HP-IL floppy disk via: HP-IL PC via one of: HP-IL and RS-232
Other
Power supply	four size N batteries or HP 82120A rechargeable battery pack

The HP-41C serial are programmable, expandable, continuous memory handheld RPN calculators fabricated by Hewlett-Packard from 1979 to 1990. The original model, HP-41C, was the first of its kind to offer alphanumeric brandish capabilities. Afterward came the HP-41CV and HP-41CX, offer more retentivity and functionality.

The alphanumeric "revolution" [edit]

The HP-41C'southward alphanumeric display allowed it to display numbers, characters, and symbols.

The alphanumeric LCD screen of the HP-41C revolutionized the style a pocket figurer could be used, providing user friendliness (for its fourth dimension) and expandability (keyboard-unassigned functions could exist spelled out alphabetically). By using an alphanumeric display, the calculator could tell the user what was going on: it could display error messages, such as showing ("Information Error") upon attempting to divide past zero instead of simply displaying a blinking null; information technology could also specifically prompt the user for arguments ("ENTER RADIUS") instead of just displaying a question marker.

Earlier calculators needed a fundamental, or central combination, for every available function. The HP-67 had three shift keys (gilt "f", blueish "grand" and blackness "h" prefix keys); the competing Texas Instruments calculators had 2 (second and INV) and close to 50 keys (the TI-59 had 45). Hewlett-Packard were constrained past their 1 byte just instruction format. The more flexible storage format for programs in the TI-59 allowed combining more keys into one didactics. The longest educational activity required eleven keypresses, re-using the shift keys four times. The TI-59 also made use of the Op key followed past ii digits to access some other 40 different functions, but the user had to remember the codes for them. Clearly, a more convenient and flexible method of executing the calculator'southward instructions was needed. The HP-41C had a relatively small keyboard, and but one shift key, just provided hundreds of functions. Every role that was not assigned to a key could be invoked through the XEQ primal (pronounced Due eastXEQTE — "execute") and spelled out in full, eastward.g. XEQ FACT for the factorial function.

The calculator had a special user mode where the user could assign whatsoever role to whatsoever fundamental if the default assignments provided by HP were not suited to a specific application. For this mode, the HP-41C came with bare keyboard templates; i.e. plastic covers with holes for the keys, so the user could annotate customized keys. Hewlett-Packard even sold a version of the calculator where hardly any keys had office names printed on them, meant for users who would exist using the HP-41C for custom calculations only (thus not needing the standard central layout at all); this version of the computer was colloquially known, within HP's Corvallis estimator team, equally a "Blanknut" (considering the development code proper name for the HP-41C'south processor was known as the "kokosnoot").^[ane]

Alphanumeric display too greatly eased editing programs, as functions were spelled out in total. Numeric-only calculators displayed programming steps every bit a list of numbers, each number generally mapped to a key on the keyboard, often via row and column coordinates. Encoding functions to the corresponding numeric codes, and vice versa, was left to the user, having to look upward the function–lawmaking combinations in a reference guide. The busy programmer quickly learned well-nigh of the codes, only having to learn the codes intimidated the beginners. In add-on to this, the user had to mentally proceed function codes dissever from numeric constants in the program listing.

The HP-41C displayed each character in a block consisting of 14 segments that could be turned on or off; a and so-chosen 14 segment brandish (similar to the much more common seven segment displays, which tin can be used to brandish digits just). The HP-41C used a liquid-crystal display instead of the ubiquitous LED displays of the era, to reduce power consumption.

While this allowed the brandish of uppercase messages, digits, and a few punctuation characters (the FOCAL character gear up), some designs needed to be twisted arbitrarily (east.g. to distinguish S from 5) and lowercase letters were unreadable (HP only provided brandish of lowercase letters a through e). HP's competitor Sharp, when introducing the PC-1211, used a dot matrix of v×seven dots and displayed the characters in principle equally we see them today on computer screens (and, in fact, many LCD screens on diverse embedded systems); this was subsequently used by HP with the HP-71B handheld computer.

The HP-41CV and CX [edit]

Many users had used all 4 ports for memory expansion, leaving no room for other modules. HP designed the Quad Retentivity Module with four times the corporeality of retentiveness, providing the maximum bachelor memory and leaving three empty ports available. The HP-41CV (V being the Roman numeral for 5) included this memory module on the main board, thus providing five times the memory of the HP-41C, and four available slots.

The internal architecture prohibited the add-on of more memory, so HP designed an extended memory module that could be seen equally secondary storage. You could non access the data directly, simply yous could transfer it to and from chief memory. To the computer (and the user), information located in the extended retention looked similar files on a modern hard disk practise for a PC (user).

The final HP-41 model, the HP-41CX, included extended memory, a built-in time module, and extended functions. It was introduced in 1983 and discontinued in 1990.

Programming [edit]

The HP-41C is keystroke programmable significant that it can recall and later execute sequences of keystrokes to solve detail issues of interest to the user. These keystroke programs, in addition to performing any functioning unremarkably bachelor on the keyboard, can also make utilize of provisional and unconditional branching and looping instructions, assuasive programs to perform repetitive operations and brand decisions.

The HP-41C besides supports indirect addressing (computed goto) with which information technology is possible to implement a Universal Turing motorcar and therefore the programming model of the HP-41C can exist considered Turing complete. The combination of indirect addressing and gotos easily led to spaghetti code.

Program steps are numbered starting from 1, but this numbering has no intrinsic pregnant and changes every bit new instructions are added or removed in the middle of a plan. A special LBL education is used to create a label that is so referenced by the user to invoke the program, or past the program itself as target of a GTO (unconditional goto) or XEQ (execute) education.

Programming example [edit]

Here is a sample programme that computes the factorial of an integer between ane and 69 (70! needing an exponent greater than 99, the calculator's maximum). The integer is entered in the X register and passed as an input parameter when the program is run. The program takes upward 2 registers, which is ≈xiv bytes.

          Step  Op-code      Comment          01    LBL'Fac      Alpha global label makes program callable by 'XEQ Fac' 02    STO 00       Store X=input parameter in annals 0 03    1            Enter 1 in X, "lifting", or "pushing", the stack: Y=input parameter (no longer used)                                                                      X=1 04    LBL 00       Local label for goto 05    RCL 00       Recollect register 0 into 10, lifting the stack: Z=input parameter (no longer used)                                                                 Y=1 or interim or final factorial                                                                 10=input parameter (N) minus effect of DSE command (-0, -ane, ..., -(N-1)) 06    *            Multiply 10 and Y, "dropping", or "popping", the stack: Y=input parameter (no longer used)                                                                           X=acting or concluding factorial 07    DSE 00          Decrement annals 0 and          Southwardkip adjacent command when register value is          Eastwardqual to 0 08    GTO 00       Go to local label 0 09    Finish          Cease program - result displayed in Ten

FOCAL [edit]

The box (meridian) in which the HP-41CV was sold with most of the manuals, programming handbooks and accessories; the power supply is not depicted

Though the programming linguistic communication used on the 41 serial is a version of the keystroke programming languages used all preceding programmable HP calculators, the range of technologies, and programming-related usability and extensibility features bachelor in 41 serial models (notably keyboard overlays, a fully remappable keyboard, I/O capabilities for storing and sharing programs, and alphanumeric support), led some users to propose a new name for the language, resulting in a contest that was won by "FOCAL" for "Forty Ane Estimator Linguistic communication".^[2] ^[three] ^[4] Every bit the proper noun FOCAL was already in utilise by the Digital Equipment Corporation, the name was never formally adopted by HP.

Synthetic programming [edit]

A large users' customs was built around the HP-41C. Enthusiasts effectually the world institute new means of programming, created their ain software (such equally a codebreaking game,^[5] and a version of Hunt the Wumpus ^[6]) and expansion modules, and sped up the clock (see overclocking). Nigh of these activities were coordinated by the PPC club and its president, Richard J. Nelson. The PPC club published the PPC Journal and produced the PPC ROM, a collection of highly optimized low-level programs for the HP-41C.

One of the discoveries of the community was that, because some FOCAL instructions were stored in memory as more than 1 byte, information technology is possible to exploit a problems in the program editor to assign foreign functions to keys. The most important office was known as the byte jumper, a fashion to step partially through programming instructions and edit them in ways that were not otherwise allowed. The use of the resulting instructions was called synthetic programming.

Through synthetic instructions, a user could access memory and special status flags reserved for the operating system, and exercise very strange things, including completely locking the machine. Information technology was possible to create sounds or display characters, and create animations non officially supported past the operating organisation. The system flags were also accessed as low-level shortcuts to boolean programming techniques. Hewlett-Packard did not officially support synthetic programming, but neither did information technology do anything to forestall it, and somewhen even provided internal documentation to the user groups.

Reception [edit]

In its December 1980 issue, BYTE mag described the HP-41C as "the nearly versatile auto e'er". The writer praised HP'south documentation every bit "among the best in the industry", and reported that the calculator was "much easier to program and debug" than the TI-59. Stating "I found the HP-41C far more pleasurable to programme and utilise than its predecessors" because of its alphanumeric display, the author concluded that it was "maybe non quite" a pocket reckoner.^[5] In the next issue, another author wrote that "The HP-41C ... is amid the programmable calculators that lie closest to the calculator borderline. Information technology comes close enough for the jargon of computers to be useful in describing it", and praised the simplicity and reliability of the card reader and compatibility with HP-67 and HP-97 software. The review criticized the inaccuracies in calculations from the lack of guard digits; "In that location is something cool most the earth's fanciest calculator not beingness able to give results authentic to more than 7 or viii decimal places".^[vii] Hewlett-Packard responded that the alleged imprecision was inherent to arithmetic on whatsoever estimator with finite precision.^[8]

Utilise on the Infinite Shuttle [edit]

NASA HP-41CV with Velcro to concur it in conveying case, 1983.

Astronaut Sally Ride on mission STS-7 with three HP-41C floating behind her

An HP-41C that flew on nine early on Infinite Shuttle missions is on display in the National Air and Infinite Museum in Washington, D.C. HP-41Cs with some special hardware configurations (the improver of Velcro strips, pre-production time module, and louder beeper, as well as the removal of parts whose outgassing could cause contamination) were carried on early Shuttle missions for the purpose of performing mundane but necessary calculations, such equally calculating the modify to the center of gravity due to fuel consumption. The HP-41C was also programmed to handle calculations usually performed by the main on-board computer, such as determining ignition times for re-entry, in the case of a main figurer failure.^[ix] ^[10]

Expandability [edit]

The functions of the calculator could be expanded by adding modules at the pinnacle of the machine. Four slots were bachelor to add more memory, pre-programmed solution packs containing programs covering applied science, surveying, physics, math, finance, games, etc. As such, an HP-41 could in fact be tailored to the personal needs of the user. Hardware extensions included a thermal printer, a magnetic carte reader (HP-67 compatible via converter software), and a barcode "wand" (reader).

Extension modules could as well add new instructions to the machine. The standard fix of mathematical functions of the 41-series was somewhat limited when compared to the functionality of some contemporary HP calculators (notably the HP-34C and the HP-15C). Amongst others, the standard role set offered no integration or root-finding capabilities and lacked support for matrices and complex numbers; these actress functions could exist added past an extension module.

Some other module, known every bit the Interface Loop allowed for connection of more than peripherals: larger printers, microcassette tape recorders, 3 1⁄2 -inch floppy disk drives, RS-232 communication interfaces, video display interfaces, etc. The Interface Loop could besides be used with the HP-71B, HP-75 and HP-110 computers.

Extension slots of the HP-41CX

HP-41 extension (or expansion) modules immune the user of an HP-41 programmable calculator to extend the functionality of the machine. The HP-41 had room for up to four expansion modules at the back of calculator.

The HP-41 was non the only calculator of its generation that immune expansion modules. The TI-58 and TI-59 also had pluggable ROM modules. The HP-41 modules were however much more versatile.

Memory modules (HP-41C only) [edit]

HP 82106A retention module for HP-41C

HP 82170A QUAD retentivity module for HP-41C

Memory modules added RAM main memory to the calculator, allowing more programming steps and/or more data registers.

The original HP-41C had a chief memory of 63 registers of seven bytes each. Each register could concur either a number, a half dozen-character string, or upward to seven program steps in the FOCAL language (program steps used a variable number of bytes).

Each memory module added 64 registers, and the calculator could hold upwardly to four of them, for a grand total of 319 registers. While this was considered huge for the time (a little more than than 2 kilobytes,) all expansion slots were used. User groups found a way to merge ii memory chips in a single module, thus freeing two expansion slots. HP designed a module holding all four in ane slot, the then-called Quad Memory Module. The afterwards HP-41CV had the quad module born.

Awarding pacs [edit]

The ROM-based awarding 'pac' modules added upwards to 4 kilobytes of read-only memory (some up to viii kilobytes, but these were just two independent 4K modules in the same box). Virtually modules held dozens of programs written in the HP-41C programming linguistic communication, FOCAL.

Programs in the ROM modules could be called from a user programme, using the ubiquitous XEQ function. In the plan code, XEQ appeared every bit "XROM" when it was used to call a ROM program.

82104A carte du jour reader [edit]

HP 82104A - bill of fare reader/writer

The carte reader was a device able to read and write small rectangular plastic cards with two magnetic strips. The card reader could copy contents of retentiveness onto magnetic cards, and later read back the data into memory.

As the HP-41C had not-volatile memory (user programs and data were non wiped out when power was off) there was no absolute need for a permanent storage device, so the card reader was optional.

Each carte held two strips of 112 bytes each, that could hold 16 data registers or up to 112 program steps. This express capacity resulted in typical programs requiring five or more magnetic cards to be saved. A full backup of the motorcar's 319 memory registers plus internal information required 11 magnetic cards (each card had to be inserted twice.)

The card reader could read magnetic cards from the earlier model HP-67. HP-67 programs were translated into HP-41C instructions, as the HP-67 and HP-41 share the same programming model and operation stack. Some instructions notwithstanding were specific to the HP-67, and the card reader provided additional instructions to emulate the 67.

Magnetic cards could be write-protected, and programs saved equally private: once loaded back, the source code for the plan could not be displayed. This fabricated magnetic cards an obvious choice for plan distribution.

However, the electrical motor put a heavy strain on the calculator batteries, and the price tag for blank cards put an fifty-fifty heavier strain on the user's wallet.

82182A time module [edit]

The time module added a real-time clock. The clock allowed utilize of real-world time in programs. The user could ready alarms that triggered calls to user programs. The alarms were able to switch the estimator on, so it was possible to create programs that executed at some point during the 24-hour interval, so switch the calculator off until the next warning. As the HP-41 was oft used every bit a data-gathering device in labs, this allowed the estimator to read data from monitored devices at specific times every 24-hour interval, without having to remain fully powered up in between readings (thus saving battery capacity).

The HP-41CX had the time module built in.

82143A thermal printer/plotter [edit]

The printer used rolls of thermal paper to print lines of upward to 24 characters. The thermal paper provided for a bluish printout, but was somewhat unstable, as the printout could vanish or the whole newspaper turn blue due to excessive heat.

The printer had some graphical capabilities, to allow the user to pattern character shapes, or even turn on or off individual pixels. However, the buffer retentivity could not hold sufficient data to impress a whole line in graphic mode, and could not alter line spacing, and so information technology was impossible to print continuous graphics in horizontal mode. The printer, nonetheless, provided some printing utilities that were able to graph a part vertically onto the narrow strip of printer paper.

82242A infrared printer interface [edit]

Instead of using the aforementioned printer, this module could be used to interface a thermal printer with an infrared interface, namely the HP 82240A and the HP 82240B. This allows for on-the-go printing without using cables - but the printer itself needs batteries besides.

82153A optical wand [edit]

The optical wand was a barcode reader shaped like a thick pen, and was designed to read lines of HP-proprietary standard barcodes into the figurer memory. The barcodes, printed in e.1000. HP solutions books, could consist of programs, numeric or alphabetical constants, and even keypresses (letting the calculator be operated without using the keyboard) — useful for diagnosing calculators where the keyboard was suspected to be faulty.

82180A extended functions module [edit]

10 Functions module 82180A for HP-41C/CV

The Extended Functions module added many functions which had long been requested by users, such as the power to programmatically assign functions to keys, repartition memory, etc.

But the most of import new part was the management of extended retentivity: while the HP-41C could theoretically access up to 1024 registers, the early design express principal retentivity to 319 registers only. The Extended Functions module added instructions to manage a banking company of additional memory in the available addressing space of the motorcar. As this memory was not directly addressable by user programs, it was seen every bit a set up of named files containing either programs or data. Programs and information registers could exist copied back and forth from the extended memory to the main retention, where they could exist accessed as usual.

Extended retentivity could besides hold ASCII files, and a rudimentary text editor was added also.

The Extended Functions module contained 124 registers of Extended memory. More could be added by ... Extended Memory modules. The HP-41CX contained the Extended Functions module as standard.

82181A extended retentivity module [edit]

10 Retentiveness module HP82181A for HP-41CX

Extended memory modules added more extended retentiveness to the HP-41C. They required an extended functions module to exist present, or the HP-41CX version of the calculator.

Each module added 238 registers of extended memory. Up to two extended memory modules could be inserted, for a k full of 124 + two*238 = 600 registers. Added to the 319 registers of principal retention, this covered practically all of the machine's 1024 addressable registers, for a total of 919 registers, or 6433 bytes.

HP82160A HP interface loop (HP-IL) module [edit]

Run across the main article on HP-IL.

Clones [edit]

DM41 et al. [edit]

The continued popularity of the HP-41CX among users prompted SwissMicros to produce a miniature computer approximating the size of an ID-i credit card (88 mm × 59 mm × seven mm) in 2015. Named DM41, it runs the original HP-41CX firmware with extended memory and realtime clock in an emulator on an ARM Cortex-M0-based NXP LPC1115 processor.^[11] Deviating from the original, it comes in a mural course cistron (as known from Hewlett-Packard's Voyager series) with rearranged keys, it features a dot-matrix brandish, switchable clock speeds, and, based on a Silicon Labs CP2102 converter chip,^[12] it comes with a USB (Mini-B)^[13] serial interface to exchange data with a PC etc. for fill-in purposes, to possibly communicate with applications (similar PC-based emulators),^[12] or to update the firmware. In December 2015, SwissMicros introduced the DM41L, a version of the computer about the same size as the calculators of the HP Voyager series. It nevertheless comes with a USB Mini-B connector. Since September 2020, its successor, the DM41X, has also been offered with an extended range of functions and a conventional design that is very close to the classic original version.

HP41CL [edit]

In addition to clones based on emulated HP-41 hardware, in that location exists at to the lowest degree one actual hardware clone of the HP-41 series. This is the HP41CL HP-41-series CPU board upgrade created by Monte Dalrymple at Systemyde.^[xiv] The HP41CL is a ground upwards redesign of the components plant on the HP-41 CPU lath, including the CPU, which is implemented on an FPGA and coded in Verilog RTL.^[xv] The HP41CL upgrade board is made as a drop-in replacement for the HP-41 serial CPU board, assuming that 1 has an HP-41 that has a compatible CPU board connector and a carve up CPU lath also.^[16] The upgrade comes with an over 600 register extended retentivity and over 320 plug-in module images.^[xiv] This is possible due to the fact that the HP41CL has over 1024 pages of 4K-give-and-take flash memory congenital in, of which over 500 pages are pre-loaded with HP-41 software, besides as the upgrade lath providing 128 RAM pages, which are made available to the user via a custom MMU.^[14] In add-on, a "turbo" manner is provided by the HP41CL upgrade board'due south "NEWT" CPU design, which allows the user to speed up their estimator past a cistron of around fifty times.^[xiv] Likewise, the HP41CL maintains full compatibility with the HP-41 series bus, and so that near plug-in modules can still be used in a fully backward compatible fashion.^[14] Additionally, Systemyde makes an HP-41 compatible timer module clone as well as a GPS receiver interface module.^[17] Furthermore, an optional RS-232 full-duplex serial connector (with a ii.5mm stereo jack physical interface) is available, if 1 has a free module slot.^[xviii]

Emulators [edit]

An emulation app for the HP-41CX running on Apple iOS. Additionally, the imitation output of the thermal printer can be displayed.

Unusually for pocket calculators, the devices withal have a fan base of operations more than than xxx years after their production was discontinued in 1989. As a consequence, emulator programs are available for a variety of operating systems, including Windows, Mac OS, Unix variants, Pocket PC, Palm OS, Apple iOS and Android.^[19]

Images [edit]

Alphanumeric display of an HP-41CX
HP-IL interface module
HP82162A thermal printer (with HP-IL connectedness)
HP82161A cassette drive with storage medium (with HP-IL connection)
Interface loop with thermal printer HP82162A (front left), a cassette drive HP82161A (back left) and an HP-41CX
HP 82163B - 32 columns video interface for HP-IL
Extension slots of an HP-41CX
HP82242A IR-interface (to a thermal printer)
HP 82104A - card reader/author for HP-41C
X Memory module HP82181A (memory extension)
Statistics module
HP 82106A memory module for HP-41C
HP 82120A battery pack for the HP-41CX with damaged NiCd cells (original)
HP 82120A battery pack for the HP-41CX (the original NiCd cells were replaced by NiMH cells)

References [edit]

^ HP documentation released to the HP-41C hobbyist community in the early 1980s; available at HP-41 Internal Documentation.
^ "Series forty File". Professional Computing Magazine. John Wiley & Sons. 1 (iii): 65. August 1984. [...] The June–Baronial 1982 issue of HP Primal Notes had a "Name-That-Language" contest for the keystroke code used on the 41. FOCAL, for Forty-One Calculator Language, was the winning entry. Although non widely recognized due to lack of publicity, information technology was supposed to be, and yet may become, the mutual description for standard keystroke language. [...]
^ Extend your HP-41. 1985. p. 12. (NB. Mentions "FOCAL".)
^ HEPAX manual. Vol. ii. 1988. p. sixteen (95). [...] 40 One CAlculator Language [...]
^ ^a ^b Carbrey, Bruce D. (December 1980). "A Pocket Computer? Sizing up the HP-41C". BYTE: 244–262.
^ Librach, Hank (February 1981). "Hunt the Wumpus with Your HP-41C". BYTE: 230, 232. Retrieved 2013-10-18 .
^ Hayes, Brian P. (January 1981). "The HP-41C: A Literate Calculator?". BYTE: 118. Retrieved 2013-10-18 .
^ Abell, Steve (April 1981). "Well-Rounded Automobile". BYTE: 16–17. Retrieved 2013-10-18 .
^ "Hewlett-Packard HP-41C Calculator". Smithsonian National Air and Space Museum. 1999-08-xviii. Archived from the original on 2000-12-10. Retrieved 2015-eleven-03 .
^ Jarett, Keith (October–Nov 1984). "HP 41 in Orbit". Professional Computing. John Wiley & Sons. 1 (4): 50–54.
^ "SwissMicros.com". Retrieved 2015-xi-02 .
^ ^a ^b "SwissMicros DM15 Scientific Calculator". JEPSPECTRO. 2017-12-22. Archived from the original on 2017-12-20. Retrieved 2018-01-04 .
^ "SwissMicros" (PDF). SwissMicros. Archived (PDF) from the original on 2017-12-twenty. Retrieved 2018-01-04 .
^ ^a ^b ^c ^d ^e "41CL Calculator". Systemyde International Corporation. Systemyde International Corporation. 2019-02-21. Retrieved 2020-12-17 .
^ "Hardware". Systemyde International Corporation. 2020-09-10. Retrieved 2020-12-17 .
^ "41CL User Transmission" (PDF). Systemyde International Corporation. 2020-12-08. Retrieved 2020-12-17 .
^ "Manuals". Systemyde International Corporation. 2020-12-08. Retrieved 2020-12-17 .
^ "HP-41CL (replacement CPU lath) Project". HP Estimator Wiki. 2017-11-28. Retrieved 2020-12-17 .
^ List of emulators for the HP-41 series , www.hp41.org

External links [edit]

Developer view of the 14 segment LCD Lawmaking of the HP41CX Calculator emulation.

Media related to HP-41C at Wikimedia Commons
SwissMicros DM41X and DM41L
HP-41CL a modded version with 50x speed 120 module integrated
The Museum of HP Calculators' article on the HP-41 serial
hp41.org – A website (and domain) defended to the HP-41
HP41 Forum
i41CX+ HP-41CX Emulator for the iPhone and iPod touch
a41CV An HP41CV simulator for the Android platform
HP-41C, HP-41CV and HP-41CX on MyCalcDB (bilingual) (database almost 1970s and 1980s pocket calculators)
Page of an HP-41CX user with photos, documents for download, printer, card reader...
C++ (linux, QT) Source-code project. Simulator HP41CX in a virtually natural look. Based on nsim-0.61 NUT Cadre by Eric Smith.
clonix41.org - A website (and domain) with some interesting enhancements for the HP-41