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
Skyles Electric Works Skyles Electric Works Skyles Electric Works was founded in California by Bob Skyles, a former Commodore engineer, to produce hardware add-ons for the Commodore PET. Like Apple Computer it began in a garage in Cupertino, but for most of the company's existence it was based in Mountain View. The first products from Skyles Electric Works were memory expansions and keyboards (the first PETs had calculator-style keys which were unsuited to touch-typing). The earliest software products were firmware, including the "Command-O" and "Disk-O-Pro", which enhanced the BASIC language of the PET. However the company also published cassette and disk-based software including