page_title: HP-41C
section_title: 82104A card reader
hierarchical_section_title: HP-41C / Expandability / 82104A card reader
caption_attribution_description: English: HP programmable calculators 41, 65, 67/97 magnetic card
context_page_description: The HP-41C series are programmable, expandable, continuous memory handheld RPN calculators 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.
context_section_description: 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.
caption: HP magnetic card
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