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 computer was designed to run business application software such as payroll. Software specifically to perform calculations as its main purpose was first written in the 1960s, and the first software package for general calculations to obtain widespread use was released in 1978. This was VisiCalc and it was called an "interactive visible calculator", but it was actually a spreadsheet, and these are now not normally known simply as calculators. The Unix version released in 1979, V7 Unix, contained a command-line accessible calculator. Calculators have been used since ancient times and until the advent of software calculators they were physical, hardware