Programmable calculator to use magnetic strips were the HP-41C and TI-59. Continuous memory does not lose its content when the calculator is switched off. With continuous memory the user can, for example, change batteries without losing the entered programs. Compact Cassettes offered a simple, inexpensive alternative to magnetic cards. Usually, an interface module, such as the Casio FA-1, was used to connect the calculator to an ordinary cassette recorder and digital data were encoded as frequency-shift keyed audio signals. Sharp and Hewlett-Packard also sold dedicated micro- or mini-cassette recorders that connected directly to the calculator. These set-ups, while being more practical and
Software calculator machines. The most recent hardware calculators are electronic hand-held devices with buttons for digits and operations, and a small window for inputs and results. The first software calculators imitated these hardware calculators by implementing the same functionality with mouse-operated, rather than finger-operated, buttons. Such software calculators first emerged in the 1980s as part of the original Macintosh operating system (System 1) and the Windows operating system (Windows 1.0). Some software calculators directly simulate one of the hardware calculators, by presenting an image that looks like the calculator, and by providing the same functionality. There is now a very wide range