View source for HP-41C

{{Short description|Hewlett-Packard handheld RPN calculator}}
{{Use dmy dates|date=April 2019|cs1-dates=y}}
{{Infobox calculator
| name         = HP-41C series
| image        = HP-41CX.jpg
| caption      = HP-41CX with magnetic card reader and thermal printer
| type         = [[Programmable calculator|Programmable]] [[Scientific calculator|scientific]]
| entry        = [[RPN input method|RPN]]
| introduced   = 1979
| discontinued = 1990
| display_type = [[Liquid crystal display|LCD]] [[fourteen-segment display]]
| display_size = 12 14-segment (alphanumeric) digits
| processor    = [[HP Nut]] core (1LF5-0002)<ref name="HP_41C_CPU">{{cite web |url=https://literature.hpcalc.org/community/hp41c41cv41cx-sm-en.pdf |title=HP-41C/CV/CX Alphanumeric Programmable Scientific Calculator, Service Manual |access-date=2022-07-01}}</ref>
| prog_lang    = [[Reverse Polish Notation|RPN]] key stroke <small>(fully merged, [[Turing complete]])</small>
| memory_data  = 63 .. 319
| memory_step  = 441 .. 2233
| conn1        = [[micro-cassette]]
| via1_1       = [[HP-IL]]
| conn2        = [[floppy disk]]
| via2_1       = HP-IL
| conn3        = PC
| via3_1       = HP-IL
| via3_2       = and [[RS-232]]
| ports        = four vendor specific
| supply       = four [[N battery|size N batteries]] or HP 82120A rechargeable battery pack
| weight       = 
| dimensions   = 
}}

The '''HP-41C''' series are programmable,  expandable, [[HP Continuous memory|continuous memory]] handheld [[Reverse Polish Notation|RPN]] [[calculator]]s made by [[Hewlett-Packard]] from 1979 to 1990. The original model, '''HP-41C''', was the first of its kind to offer [[alphanumeric]] display capabilities. Later came the '''HP-41CV''' and '''HP-41CX''', offering more memory and functionality.

== The alphanumeric "revolution" ==
[[File:LCD Display of HP41CX (cropped).jpg|thumb|The HP-41C's alphanumeric display allowed it to display numbers, characters, and symbols.]]
[[File:HP-41CV Calculator.jpg|thumb|upright=0.9|The HP-41CV had a memory five times larger than that of the first model HP-41C. On the lower, inclined flank of the keys, the alphanumeric characters are printed in blue, which are accessible after pressing the "ALPHA" key top right.]]

The [[alphanumeric]] [[liquid crystal display|LCD]] screen of the HP-41C revolutionized the way a pocket calculator could be used, providing user friendliness (for its time) and expandability (keyboard-unassigned functions could be 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 ("<samp>DATA ERROR</samp>") upon attempting to divide by zero instead of simply displaying a blinking zero; it could also specifically prompt the user for arguments ("<samp>ENTER RADIUS</samp>") instead of just displaying a question mark.

Earlier calculators needed a key, or key combination, for every available function. The [[HP-67]] had three shift keys (gold "f", blue "g" and black "h" prefix keys); the competing [[Texas Instruments]] calculators had two ({{key top|2nd}} and {{key top|INV}}) and close to 50 keys (the [[TI-59]] had 45). Hewlett-Packard were constrained by their one byte only instruction format. The more flexible storage format for programs in the [[TI-59]] allowed combining more keys into one instruction. The longest instruction required eleven keypresses, re-using the shift keys four times. The TI-59 also made use of the {{key top|Op}} key followed by two digits to access another 40 different functions, but the user had to remember the codes for them. Clearly, a more convenient and flexible method of executing the calculator's instructions was needed. The HP-41C had a relatively small keyboard, and only one shift key, but provided hundreds of functions. Every function that was not assigned to a key could be invoked through the {{key top|XEQ}} key (pronounced ''E'''XEQ'''TE''&nbsp;&mdash; "execute") and spelled out in full, e.g. {{key top|XEQ}} FACT for the [[factorial]] function.

The calculator had a special user mode where the user could assign any function to any key if the default assignments provided by HP were not suited to a specific application. For this mode, the HP-41C came with blank 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 function names printed on them, meant for users who would be using the HP-41C for custom calculations only (thus not needing the standard key layout at all); this version of the calculator was colloquially known, within HP's Corvallis calculator team, as a "Blanknut" (because the development code name for the HP-41C's processor was known as the "coconut").<ref name="Coconut"/>

Alphanumeric display also greatly eased editing programs, as functions were spelled out in full. Numeric-only calculators displayed programming steps as 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 up the function&ndash;code combinations in a reference guide. The busy programmer quickly learned most of the codes, but having to learn the codes intimidated the beginners. In addition to this, the user had to mentally keep function codes separate 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 so-called [[fourteen segment display]] (similar to the much more common [[seven segment display]]s, which can be used to display digits only). The HP-41C used a liquid-crystal display instead of the ubiquitous [[light-emitting diode|LED]] displays of the era, to reduce power consumption.

While this allowed the display of uppercase letters, digits, and a few punctuation characters (the [[FOCAL character set]]), some designs needed to be twisted arbitrarily (e.g. to distinguish S from 5) and lowercase letters were unreadable (HP only provided display of lowercase letters a through e). HP's competitor [[Sharp Electronics|Sharp]], when introducing the [[Sharp PC-1211|PC-1211]], used a [[dot matrix]] of 5×7 dots and displayed the characters in principle as we see them today on computer screens (and, in fact, many LCD screens on various [[embedded system]]s); this was later used by HP with the [[HP-71B]] handheld computer.

== The HP-41CV and CX ==
Many users had used all four ports for memory expansion, leaving no room for other modules. HP designed the ''Quad Memory Module'' with four times the amount of memory, providing the maximum available 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 addition of more memory, so HP designed an extended memory module that could be seen as secondary storage. The data could not be access directly, but it was possible to transfer data to and from main memory. To the calculator (and the user), data located in the extended memory looked like files on a modern hard disk do 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 ==

The HP-41C is [[keystroke programmable]] meaning that it can remember and later execute sequences of keystrokes to solve particular problems of interest to the user. These keystroke programs, in addition to performing any operation normally available on the keyboard, can also make use of conditional and unconditional branching and looping instructions, allowing programs to perform repetitive operations and make decisions.

The HP-41C also supports indirect addressing ([[Computed GOTO|computed goto]]) with which it is possible to implement a [[Universal Turing machine]] and therefore the programming model of the HP-41C can be 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 meaning and changes as new instructions are added or removed in the middle of a program. A special LBL instruction is used to create a label that is then referenced by the user to invoke the program, or by the program itself as target of a GTO (unconditional goto) or XEQ (execute) instruction.

=== Programming example ===
Here is a sample program that computes the factorial of an integer between 1 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 up two registers, which is ≈14 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 register 00
 03    1            Enter 1 in X, "lifting", or "pushing", the [[Stack (abstract data type)|stack]]: Y=input parameter (no longer used)
                                                                      X=1
 04    LBL 00       Local label for goto
 05    RCL 00       Recall register 00 into X, lifting the stack: Z=input parameter (no longer used)
                                                                 Y=1 or interim or final factorial
                                                                 X=input parameter (N) minus effect of DSE command (-0, -1, ..., -(N-1))
 06    *            Multiply X and Y, "dropping", or "popping", the stack: Y=input parameter (no longer used)
                                                                           X=interim or final factorial
 07    DSE 00       '''D'''ecrement register 00 and '''S'''kip next command when register value is '''E'''qual to 0
 08    GTO 00       Go to local label 00
 09    END          End program - result displayed in X

=== FOCAL ===
[[File:Programmable Calculator HP-41CV with box, included manuals and leather pouch (background removed).jpg|thumb|upright|The box (top) 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 language used on the 41 series is a version of the keystroke programming languages used in all preceding programmable HP calculators, the range of technologies, and programming-related usability and extensibility features available in 41 series 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 competition that was won by "FOCAL" for "Forty One Calculator Language".<ref name="Wiley_1984"/><ref name="Extend_1985"/><ref name="HEPAX_1988"/> As the name FOCAL was [[FOCAL (programming language)|already in use]] by the [[Digital Equipment Corporation]], the name was never formally adopted by HP.

== Synthetic programming ==
A large user community was built around the HP-41C. Enthusiasts around the world found new ways of programming, created their own software (such as a codebreaking game,{{R|carbrey198012}} and a version of ''[[Hunt the Wumpus]]''<ref name="librach198102"/>) and expansion modules, and sped up the clock (see [[overclocking]]). Most 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 [[variable-length instruction set|more than one byte]], it is possible to exploit a bug in the program editor to assign strange functions to keys. The most important function was known as the [[byte jumper]] or [[byte grabber]], a way 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 (HP-41)|synthetic programming]]''.

Through synthetic instructions, a user could access memory and special status flags reserved for the operating system, and do very strange things, including completely locking the machine. It was possible to create sounds or display characters, and create animations not officially supported by the operating system. 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 it do anything to prevent it, and eventually even provided internal documentation to the user groups.

== Reception ==
In its December 1980 issue, ''[[Byte (magazine)|BYTE]]'' magazine described the HP-41C as "the most versatile machine ever". The author praised HP's documentation as "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 program and use than its predecessors" because of its alphanumeric display, the author concluded that it was "maybe not quite" a pocket computer.<ref name="carbrey198012" /> In the next issue, another author wrote that "The HP-41C&nbsp;... is among the programmable calculators that lie closest to the computer borderline. It 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 digit]]s; "There is something absurd about the world's fanciest calculator not being able to give results accurate to more than seven or eight decimal places".<ref name="hayes198101" /> Hewlett-Packard responded that the alleged imprecision was inherent to arithmetic on any computer with finite precision.<ref name="abell198104" />

== Use on the Space Shuttle ==
[[File:NASA HP-41CV.jpg|thumb|NASA HP-41CV with Velcro to hold it in carrying case, 1983]]
[[File:STS007-14-629.jpg|thumb|left|[[Sally Ride]], the first female [[astronaut]] of the USA, on [[Space Shuttle]] mission [[STS-7]] (1983) with three HP-41C floating beside her]]
An HP-41C that flew on nine early [[Space Shuttle]] missions is on display in the [[National Air and Space Museum]] in Washington, D.C. HP-41Cs with some special hardware configurations (the addition 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 as calculating the change 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 computer failure.<ref name="NASM" /><ref name="Jarett" />

== Expandability ==
The functions of the calculator could be expanded by adding modules at the top of the machine. Four slots were available to add more memory, pre-programmed solution packs containing programs covering engineering, 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 card reader (HP-67 compatible via converter software), and a barcode "wand" (reader).

Extension modules could also add new instructions to the machine. The standard set 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]]). Among others, the standard function set offered no integration or root-finding capabilities and lacked support for matrices and complex numbers; these extra functions could be added by an extension module.

Another module, known as the [[HP-IL|Interface Loop]] allowed for connection of more peripherals: larger printers, [[microcassette]] tape recorders, 3{{frac|1|2}}-inch [[floppy disk]] drives, [[RS-232]] communication interfaces, video display interfaces, etc. The Interface Loop could also be used with the [[HP-71B]], [[HP-75]] and [[HP-110]] computers.

[[File:0978 - HP41CX Expansion Slots.jpg|thumb|Extension slots of the HP-41CX]]
'''HP-41 extension (or expansion) modules''' allowed 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 not the only calculator of its generation that allowed 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) ===
[[File:1028 - HP82106A.jpg|thumb|HP 82106A memory module for HP-41C]]
[[File:HP-41C QUAD MEMORY.JPG|thumb|HP 82170A QUAD memory module for HP-41C]]

Memory modules added [[random-access memory|RAM]] main memory to the calculator, allowing more programming steps and/or more data registers.

The original HP-41C had a main memory of 63 registers of 7 [[byte]]s each. Each register could hold either a number, a 6-character string, or up to seven program steps in the [[Focal (HP-41)|FOCAL]] language (program steps used a variable number of bytes).

Each memory module added 64 registers, and the calculator could hold up to four of them, for a grand total of 319 registers. While this was considered huge for the time (a little more than 2 [[kilobyte]]s,) all expansion slots were used. User groups found a way to merge two memory chips in a single module, thus freeing two expansion slots. HP designed a module holding all four in one slot, the so-called ''Quad Memory Module''. The later HP-41CV had the quad module built-in.

=== Application pacs ===
The [[read-only memory|ROM]]-based application 'pac' modules added up to 4 kilobytes of read-only memory (some up to 8 kilobytes, but these were simply two independent 4K modules in the same box). Most modules held dozens of programs written in the HP-41C programming language, FOCAL.

Programs in the ROM modules could be called from a user program, using the ubiquitous XEQ function. In the program code, XEQ appeared as "<code>XROM</code>" when it was used to call a ROM program.

=== 82104A card reader ===
[[File:Card reader-writer 82104A for calculator HP41C.jpg|thumb|HP 82104A&nbsp;- card reader/writer]]
[[File:HP magnetic card.jpg|thumb|HP magnetic card]]
The card reader was a device able to read and write small rectangular plastic cards with two magnetic strips. The card reader could copy contents of memory onto magnetic cards, and later read back the data into memory.

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

Each card held two strips of 112 bytes each, that could hold 16 data registers or up to 112 program steps. This limited capacity resulted in typical programs requiring five or more magnetic cards to be saved. A full backup of the machine's 319 memory registers plus internal data 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 however 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 as private: once loaded back, the source code for the program could not be displayed. This made magnetic cards an obvious choice for program distribution.

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

=== 82182A time module ===
The time module added a real-time clock. The clock allowed use of real-world time in programs. The user could set alarms that triggered calls to user programs. The alarms were able to switch the calculator on, so it was possible to create programs that executed at some point during the day, then switch the calculator off until the next alarm. As the HP-41 was often used as a data-gathering device in labs, this allowed the calculator to read data from monitored devices at specific times every day, 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 ===
The printer used rolls of thermal paper to print lines of up to 24 characters. The thermal paper provided for a bluish printout, but was somewhat unstable, as the printout could vanish or the whole paper turn blue due to excessive heat.

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

=== 82242A infrared printer interface ===
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&nbsp;- but the printer itself needs batteries as well.

=== 82153A optical wand ===
[[File:Hewlett-Packard barcode reader 'Optical Wand' for HP-41 calculators.jpg|thumb|HP 82153A&nbsp;- optical wand]]
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 calculator memory. The barcodes, printed in e.g. HP solutions books, could consist of programs, numeric or alphabetical constants, and even keypresses (letting the calculator be operated without using the keyboard)&nbsp;&mdash; useful for diagnosing calculators where the keyboard was suspected to be faulty.

=== 82180A extended functions module ===
[[File:HP-41C Extended Functions Memory Module.JPG|thumb|X Functions module 82180A for HP-41C/CV]]

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

But the most important new function was the management of extended memory: while the HP-41C could theoretically access up
to 1024 registers, the early design limited main memory to 319 registers only. The Extended Functions module added instructions to manage a bank of additional memory in the available addressing space of the machine. As this memory was not directly
addressable by user programs, it was seen as a set of named files containing either programs or data. Programs and data registers could
be copied back and forth from the extended memory to the main memory, where they could be accessed as usual.

Extended memory could also 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 memory module ===
[[File:0986 - HP41CX X Memory HP82181A.jpg|thumb|X Memory module HP82181A for HP-41CX]]
Extended memory modules added more extended memory to the HP-41C. They required an extended functions module to be 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 grand total of 124 + 2*238 = 600 registers. Added to the 319 registers of main memory, 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 ===
''See the main article on [[HP-IL]].''

== Clones ==
=== {{anchor|DM41|DM41X|DM41L}} DM41 et al. ===
The continued popularity of the HP-41CX among users prompted [[SwissMicros]] to produce a miniature calculator approximating the size of an [[ID-1 format|ID-1]] credit card (88&nbsp;mm&nbsp;× 59&nbsp;mm&nbsp;× 7&nbsp;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.<ref name="SM"/> Deviating from the original, it comes in a landscape form factor (as known from Hewlett-Packard's [[HP Voyager series|Voyager series]]) with rearranged keys, it features a dot-matrix display, switchable <!-- fonts and -->clock speeds, and, based on a [[Silicon Labs]] CP2102<!-- CP2102 or CP2102N? --> converter chip,<ref name="DM15"/> it comes with a [[USB]] ([[USB Mini-B|Mini-B]])<ref name="SM_Serial"/> serial interface to exchange data with a PC etc. for backup purposes, to possibly communicate with applications (like PC-based emulators),<ref name="DM15"/> or to update the firmware. In December 2015, SwissMicros introduced the ''DM41L'', a version of the calculator about the same size as the calculators of the HP Voyager series. It still 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.

=== {{anchor|HP41CL|41CL}} HP41CL ===
In addition to clones based on emulated HP-41 hardware, there exists at least one actual hardware clone of the HP-41 series. This is the HP41CL HP-41-series CPU board upgrade created by [[Monte Dalrymple|Monte&nbsp;Dalrymple]] at Systemyde.<ref name="41CL_1">{{cite web |title=41CL Calculator |url=http://www.systemyde.com/hp41/ |date=21 February 2019 |website=Systemyde International Corporation |publisher=Systemyde International Corporation |access-date=17 December 2020}}</ref> The HP41CL is a ground up redesign of the components found on the HP-41 CPU board, including the CPU, which is implemented on an [[FPGA]] and coded in [[Verilog]] [[Register-transfer level|RTL]].<ref name="41CL_2">{{cite web |title=Hardware |url=http://www.systemyde.com/hp41/hardware.html |date=10 September 2020 |website=Systemyde International Corporation |access-date=17 December 2020}}</ref> The HP41CL upgrade board is made as a drop-in replacement for the HP-41 series CPU board, assuming that one has an HP-41 that has a compatible CPU board connector and a separate CPU board as well.<ref name="41CL_3">{{cite web |title=41CL User Manual |url=http://www.systemyde.com/pdf/sy41cl.pdf |date=8 December 2020 |website=Systemyde International Corporation |access-date=17 December 2020}}</ref> The upgrade comes with an over 600 register extended memory and over 320 plug-in module images.<ref name="41CL_1" /> This is possible due to the fact that the HP41CL has over 1024 pages of 4K-word flash memory built in, of which over 500 pages are pre-loaded with HP-41 software, as well as the upgrade board providing 128 RAM pages, which are made available to the user via a custom [[Memory Management Unit|MMU]].<ref name="41CL_1" /> In addition, a "turbo" mode is provided by the HP41CL upgrade board's "NEWT" CPU design, which allows the user to speed up their calculator by a factor of around 50 times.<ref name="41CL_1" /> Also, the HP41CL maintains full compatibility with the HP-41 series bus, so that most plug-in modules can still be used in a fully backward compatible fashion.<ref name="41CL_1" /> Additionally, Systemyde makes an HP-41 compatible timer module clone as well as a [[Global Positioning System|GPS]] receiver interface module.<ref name="41CL_4">{{cite web |title=Manuals |url=http://www.systemyde.com/hp41/manuals.html |date=8 December 2020 |website=Systemyde International Corporation |access-date=17 December 2020}}</ref> Furthermore, an optional RS-232 full-duplex serial connector (with a 2.5mm stereo jack physical interface) is available, if one has a free module slot.<ref name="41CL_5">{{cite web |title=HP-41CL (replacement CPU board) Project |url=http://www.wiki4hp.com/doku.php?id=41cl:replacement_cpu_board |archive-url=https://web.archive.org/web/20110913122752/http://www.wiki4hp.com/doku.php?id=41cl:replacement_cpu_board |url-status=usurped |archive-date=13 September 2011 |date=28 November 2017 |website=HP Calculator Wiki |access-date=17 December 2020}}</ref>

== Emulators ==
[[File:Emulator of HP-41CX on iPhone 6s.jpg|thumb|upright=0.8|An emulation [[Mobile Application|app]] for the HP-41CX running on Apple [[iOS]]. Additionally, the simulated output of the [[thermal printer]] can be displayed.]]
Unusually for pocket calculators, the devices still have a fan base more than 30 years after their production was discontinued in 1989. As a result, [[emulator]] programs are available for a variety of operating systems, including [[Microsoft Windows|Windows]], [[Mac OS]], [[Unix]] variants, [[Microsoft Pocket PC|Pocket PC]], [[Palm OS]], [[iOS|Apple iOS]] and [[Android (operating system)|Android]].<ref>'' [http://www.hp41.org/Emulation.cfm List of emulators for the HP-41 series] '', www.hp41.org </ref>

== Images ==
<gallery widths=180>
File:0934 - HP41CX.jpg|Alphanumeric display of an HP-41CX
File:Interface loop module HP-IL for connecting HP-41 calculators with peripheral devices.jpg|HP-IL interface module
File:Thermal printer HP82162A and IL-Loop and HP41CX.jpg|HP82162A thermal printer (with HP-IL connection)
File:Digital cassette drive HP82161A for HP-41 calculator series.jpg|HP82161A cassette drive with storage medium (with HP-IL connection)
File:HP-41CX connected to thermal printer and digital cassette drive via HP-IL interface loop.jpg|Interface loop with thermal printer HP82162A (front left), a cassette drive HP82161A (back left) and an HP-41CX
File:Rear connectors of video interface HP82163B for HP-41 calculators w. TV-UHF and AV output.jpg|HP 82163B&nbsp;- 32 columns video interface for HP-IL
File:0978 - HP41CX Expansion Slots.jpg|Extension slots of an HP-41CX
File:0943 - HP82242A IR-Interface.jpg|HP82242A IR-interface (to a thermal printer)
File:Card reader-writer 82104A for calculator HP41C.jpg|HP 82104A&nbsp;- card reader/writer for HP-41C
File:0986 - HP41CX X Memory HP82181A.jpg|X Memory module HP82181A (memory extension)
File:0992 - HP41CX Stat I.jpg|Statistics module
File:1028 - HP82106A.jpg|HP 82106A memory module for HP-41C
File:1022 - HP82120A.jpg|HP 82120A battery pack for the HP-41CX with damaged NiCd cells (original)
File:0995 - HP41CX Bat Pack.jpg|HP 82120A battery pack for the HP-41CX (the original NiCd cells were replaced by NiMH cells)
</gallery>

== See also ==
* [[FOCAL character set]]
* [[HP calculators]]
* [[NOMAS (support)]]

== References ==
{{Reflist|refs=
<ref name="Coconut">HP documentation released to the HP-41C hobbyist community in the early 1980s; available at [http://www.hp41.org/LibView.cfm?Command=List&CategoryID=20 HP-41 Internal Documentation].</ref>
<ref name="librach198102">{{cite journal |author-last=Librach |author-first=Hank |title=Hunt the Wumpus with Your HP-41C |journal=[[Byte (magazine)|BYTE]] |date=February 1981 |pages=230, 232 |url=https://archive.org/stream/byte-magazine-1981-03/1981_03_BYTE_06-03_Programming_Methods#page/n231/mode/2up |access-date=2013-10-18}}</ref>
<ref name="carbrey198012">{{Cite journal |author-last=Carbrey |author-first=Bruce D. |date=December 1980 |title=A Pocket Computer? Sizing up the HP-41C |journal=[[Byte (magazine)|BYTE]] |pages=244–262 |url=https://archive.org/stream/byte-magazine-1980-12/1980_12_BYTE_05-12_Adventure#page/n245/mode/2up}}</ref>
<ref name="hayes198101">{{cite journal |author-last=Hayes |author-first=Brian P. |title=The HP-41C: A Literate Calculator? |journal=[[Byte (magazine)|BYTE]] |date=January 1981 |pages=118 |url=https://archive.org/stream/byte-magazine-1981-01/1981_01_BYTE_06-01_Hand-held_Computers#page/n119/mode/2up |access-date=2013-10-18}}</ref>
<ref name="abell198104">{{cite journal |author-last=Abell |author-first=Steve |pages=16–17 |title=Well-Rounded Machine |journal=[[Byte (magazine)|BYTE]] |date=April 1981 |url=https://archive.org/stream/byte-magazine-1981-04/1981_04_BYTE_06-04_Future_Computers#page/n17/mode/2up |access-date=2013-10-18}}</ref>
<ref name="NASM">{{cite web |title=Hewlett-Packard HP-41C Calculator |date=1999-08-18 |website=Smithsonian National Air and Space Museum |url=http://www.nasm.si.edu/nasm/dsh/artifacts/GC-hewlett-.htm |access-date=2015-11-03 |archive-url=https://web.archive.org/web/20001210140300/http://www.nasm.si.edu/nasm/dsh/artifacts/GC-hewlett-.htm |archive-date=2000-12-10}}</ref>
<ref name="Jarett">{{cite journal |author-last=Jarett |author-first=Keith |title=HP 41 in Orbit |date=October–November 1984 |volume=1 |number=4 |pages=50–54 |journal=Professional Computing |publisher=[[John Wiley & Sons]] |url=https://paxer.net/voyager/docs/hp41-in-orbit.pdf |url-status=live |archiveurl=https://web.archive.org/web/20220326183442/https://paxer.net/voyager/docs/hp41-in-orbit.pdf |archivedate=2022-03-26 |access-date=2024-01-08 }}</ref>
<ref name="SM">{{Cite web |title=SwissMicros.com |url=http://www.swissmicros.com/ |access-date=2015-11-02}}</ref>
<ref name="DM15">{{cite web |title=SwissMicros DM15 Scientific Calculator |date=2017-12-22 |website=JEPSPECTRO |url=http://www.jepspectro.com/htm/dm15.htm |access-date=2018-01-04 |url-status=live |archive-url=https://web.archive.org/web/20171220072130/http://www.jepspectro.com/htm/dm15.htm |archive-date=2017-12-20}}</ref>
<ref name="SM_Serial">{{cite web |title=SwissMicros |website=SwissMicros |url=https://www.swissmicros.com/manuals/swissmicros_serial_guide_v1.63.pdf |access-date=2018-01-04 |url-status=live |archive-url=https://web.archive.org/web/20171220034706/https://www.swissmicros.com/manuals/swissmicros_serial_guide_v1.63.pdf |archive-date=2017-12-20}}</ref>
<ref name="Wiley_1984">{{cite journal |date=August 1984 |journal=Professional Computing Magazine |publisher=[[John Wiley & Sons]] |volume=1 |number=3 |page=65 |title=Series 40 File |quote=[...] The June–August 1982 issue of [[HP Key Notes]] had a "Name-That-Language" contest for the keystroke code used on the [[HP-41|41]]. FOCAL, for {{underline|F}}orty-{{underline|O}}ne {{underline|Ca}}lculator {{underline|L}}anguage, was the winning entry. Although not widely recognized due to lack of publicity, it was supposed to be, and yet may become, the common description for standard keystroke language. [...]}}</ref>
<ref name="Extend_1985">{{cite book |title=Extend your HP-41 |page=12 |date=1985}} (NB. Mentions "FOCAL".)</ref>
<ref name="HEPAX_1988">{{cite book |title=HEPAX manual |date=1988 |volume=2 |page=16 (95) |quote=[...] Forty One CAlculator Language [...]}}</ref>
}}

== Further reading ==
* {{cite book |title=HP-41C Operating Manual - A Guide for the Experienced User |publisher=[[Hewlett-Packard Company]] |date=June 1980 |id=00041-90259 |url=http://www.decadecounter.com/vta/pdf/HP%2041C%20Operating%20Manual.pdf |access-date=2018-01-04 |url-status=usurped |archive-url=https://web.archive.org/web/20180104042855/http://www.decadecounter.com/vta/pdf/HP%2041C%20Operating%20Manual.pdf |archive-date=2018-01-04}}
* {{cite book |author-last=Emery |author-first=Ken |title=HP-41 MCode for Beginners |date=1985 |location=Berkeley, USA |publisher=Synthetix |isbn=0-9612174-7-2}}
* {{cite book |author-last=Mier-Jędrzejowicz |author-first=Włodzimierz "Włodek" Anthony Christopher |title=Extend Your HP-41 |date=1986 |location=Berkeley, USA |publisher=Synthetix |isbn=0-9510733-0-3}}
* {{cite book |editor-first1=Stefan |editor-last1=Fegert |editor-first2=Heinz |editor-last2=Dalkowski |author-first1=Burkhard |author-last1=Oerttel |author-first2=Reinhold |author-last2=Hümpfner |author-first3=Bernhard |author-last3=Meier |author-first4=Michael |author-last4=Schilli |author-first5=Andreas |author-last5=Weber |author-first6=Frank |author-last6=Leissner |author-first7=Axel |author-last7=Kaiser |author-first8=Reinhard |author-last8=Strewinski |author-first9=Sebastian |author-last9=von Borries |author-first10=Heinz |author-last10=Dalkowski |author-first11=Stefan |author-last11=Fegert |title=Eine Programmsammlung für den HP-41 |trans-title=A Program Collection for the HP-41 |publisher={{ill|Heldermann Verlag|de}} |location=Berlin, Germany |date=2014 |orig-year=1989 |isbn=978-3-88538-809-8 |language=German |url=http://www.mh-aerotools.de/hp/heldermann/Eine%20Programmsammlung%20fuer%20den%20HP-41.pdf |access-date=2018-01-04 |url-status=live |archive-url=https://web.archive.org/web/20180104042911/http://www.mh-aerotools.de/hp/heldermann/Eine%20Programmsammlung%20fuer%20den%20HP-41.pdf |archive-date=2018-01-04}}
* {{cite book |author-last=Wickes |author-first=William C. |title=Synthetic Programming on the HP-41C |date=1980 |location=Corvallis, USA |publisher=Larken Publications |isbn=978-0962525803}}

== External links ==
[[File:HP41CX.png|thumb|right|Developer view of the 14 segment LCD Code of the HP41CX Calculator emulation]]
* {{Commons category-inline|HP-41C}}
* [https://www.swissmicros.com/product/dm41x SwissMicros DM41X] and [https://www.swissmicros.com/product/dm41l DM41L]
* [http://systemyde.com/hp41 HP-41CL a modded version with 50x speed 120 module integrated]
* [http://www.hpmuseum.org/hp41.htm The Museum of HP Calculators' article on the HP-41 series]
* [http://www.hp41.org hp41.org] &ndash; A website (and domain) dedicated to the HP-41
* [http://forum.hp41.org HP41 Forum]
* [https://apps.apple.com/app/id289068865 i41CX+] HP-41CX Emulator for the iPhone and iPod touch
* [http://android41cv.sourceforge.net/ a41CV] An HP41CV simulator for the Android platform
* [http://mycalcdb.free.fr/main.php?l=0&id=802 HP-41C], [http://mycalcdb.free.fr/main.php?l=0&id=805 HP-41CV] and [http://mycalcdb.free.fr/main.php?l=0&id=821 HP-41CX] on [http://mycalcdb.free.fr MyCalcDB (bilingual)] (database about 1970s and 1980s pocket calculators)
* [http://gtello.pagesperso-orange.fr/hp41_e.htm Page of an HP-41CX user] with photos, documents for download, printer, card reader...
* [https://sourceforge.net/projects/hp41cx C++ (linux, QT) Source-code project.] Simulator HP41CX in a nearly natural look. Based on nsim-0.61 NUT Core by Eric Smith.
* [http://www.clonix41.org/ clonix41.org]&nbsp;- A website (and domain) with some interesting enhancements for the HP-41

{{HP calculators}}
{{Authority control}}

[[Category:HP programmable calculators|41]]
[[Category:Computer-related introductions in 1979]]