Kansas City standard
The Kansas City standard (KCS), or Byte standard, is a digital data format for audio cassette drives. Byte magazine sponsored a symposium in November 1975 in Kansas City, Missouri to develop a standard for storage of digital microcomputer data on inexpensive consumer quality cassettes, at a time when floppy disk drives cost more than $1,000 USD each (today more than $4500 USD). Although the standard had existed from the earliest days of the microcomputer revolution, very few systems are said to have used it as their standard.
Early microcomputers generally used punched tape for program storage, an expensive option. Computer consultant Jerry Ogdin conceived the use of audio tones on a cassette to replace the paper tapes. He took the idea to Les Solomon, editor of Popular Electronics magazine, who was similarly frustrated by punched tapes. In September 1975 the two co-authored an article on the HITS (Hobbyists' Interchange Tape System), using two tones to represent 1s and 0s. Soon after a number of manufacturers started using similar approaches, although each of these systems were incompatible.
Wayne Green, who had just started Byte magazine, wanted all the manufacturers to get together and produce a single cassette standard. The site picked was Kansas City, Missouri. The two-day meeting was attended by 18 people who settled on a system based on Don Lancaster's design, published in Byte magazine's first issue. After the meeting, Lee Felsenstein (Processor Technology) and Harold Mauch (Percom) wrote the standard.
A cassette interface is similar to a modem connected to a serial port. The 1s and 0s from the serial port are converted to audio tones using audio frequency-shift keying (AFSK). A '0' bit is represented as four cycles of a 1200 Hz sine wave, and a '1' bit as eight cycles of 2400 Hz. This gives a data rate of 300 baud. Each frame starts with one start bit (a '0') followed by eight data bits (least significant bit first) followed by two stop bits ('1's). So each frame is 11 bits, for a data rate of 27 3⁄11 bytes per second.
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