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The alphanumeric LCD screen of the HP-41C revolutionized the way you could use a calculator, 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 meaningful error messages ("ZERO DIVIDE") instead of simply a blinking zero; it could also verbally prompt the user for arguments ("ENTER RADIUS") 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; the competing Texas Instruments calculators had two (2nd and INV) and over 50 keys. 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 XEQ key (pronounced EXEQTE — "execute") and spelled out in full, e.g. 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 assignations provided by HP didn't suit him¹. For this mode, the HP-41C came with blank keyboard templates; i.e. plastic covers with holes for the keys, so the user could write his own key assignments near the affected key(s). Hewlett-Packard even sold a version of the calculator where almost no key had function name printed on it, meant for users who would be using the HP-41C for custom calculations only (thus not needing the standard key layout at all).
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 mapped to a key on the keyboard. Encoding functions to the corresponding numeric codes, and vice versa, was left to the user, having to look up the function–code combinations in a reference guide. 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 displays, which can be used to display digits only). The HP-41C used an LCD display instead of the ubiquitous LED displays of the era, to reduce power consumption.
While this allowed the display of uppercase letters, digits, and a few punctuation characters, 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, when introducing the 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 systems); this was later used by HP with the HP-71 handheld computer.
See main article HP-41 Extension Module
The functions of the calculator could be expanded by adding modules at the back 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. Hardware extensions included a thermal printerDirect thermal printers create an image by selectively heating coated paper when the paper passes over the thermal print head. The coating turns black in the areas where it is heated, creating the image. More recently, two-color direct thermal printers ha, a magnetic card reader (HP-67 compatible via converter software), and a barcode "wand" (reader).
Another module, known as the Interface LoopThe HP-IL Hewlett-Packard Interface Loop is a short range network cable enabling several devices such as printers, floppy disk drives, tape readers, etc. to be connected to the HP-41C programmable calculator. The HP-IL had a master controller, the HP-IL e allowed for connection of more peripherals: larger printers, microcassetteA microcassette is a smaller format compact audio cassette. Microcassettes can only be recorded by professional tape recorders used by recording studios or by consumer devices supporting the format and having a recording mode—such as dictaphones, which re tape recorders, 3½" floppy diskA floppy disk is a data storage device that comprises a circular piece of thin, flexible (hence "floppy") magnetic storage medium encased in a square or rectangular plastic wallet. Floppy disks are read and written by a floppy disk drive or FDD not to be drives, RS-232RS-232 (also referred to as EIA RS-232C or V. 24 is a standard for serial binary data interchange between a DTE ( Data terminal equipment) and a DCE ( Data communication equipment). It is commonly used in personal computer serial ports. History This stand communication interfaces, video display interfaces, etc. The Interface Loop could also be used with the HP-71 computer.
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