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 over $1000 USD each.

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 Data Company) 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.

The February 1976 issue of Byte had a report on the symposium and the March issue featured two hardware examples by Don Lancaster and Harold Mauch. The 300 baud rate was reliable but slow. (The typical 8-kilobyte BASIC program took five minutes to load.) Most audio cassette circuits would support higher speeds.

Processor Technology developed the popular CUTS (Computer Users' Tape Standard) which worked at either 300 or 1200 baud. They provided the S-100 bus CUTS Tape I/O interface board which offered both CUTS and Kansas City standard support to any S-100 system. Processor Technology also sold many programs on cassette tape. CUTS format on one side, and Kansas City standard on the other side.