Kansas City Standard

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An audio cassette from TDK

The Kansas City Standard ( KCS ), or byte standard , is a digital data format for audio cassettes that can be written and read with a simple cassette recorder .

History of origin

The American Byte Magazine supported a symposium in Kansas City, Missouri (USA) in November 1975 , at which a standard for the storage of digital data on inexpensive audio cassettes was to be developed. At that time disk drives cost more than DM 3000, -.

The 18 participants in the meeting agreed on a system, the design of which was based on a proposal by Don Lancaster , which was described in the first issue of Byte Magazine . After the meeting, the standard was written by Lee Felsenstein ( Processor Technology ) and Harold Mauch ( Percom Data Company ).

In February 1976 Byte Magazine reported on the symposium and in March published two circuits of the cassette interface by Don Lancaster and Harold Mauch. The data rate of 300 baud was slow but reliable (loading an 8 kilobyte BASIC interpreter took five minutes). Most cassette recorders could already work with higher data rates at that time.

Description of the standard

A cassette interface works on the same principle as a modem connected to a serial interface . The digital 0 and 1 from the serial interface are converted into tones. The principle of frequency shift keying is used. A '0' is represented by four complete waves of a 1200 Hz sine curve and a '1' by eight complete waves of 2400 Hz. This results in a data transfer rate of 300 baud .

The carrier frequency (2400 Hz) must be stored on the tape for at least 30 seconds before data transmission; this is intended to support synchronization of the cassette interface with the cassette recorder.

Each data packet begins with a start bit ('0'), which is then followed by up to eight data bits ( LSB , i.e. the least significant bits first). The data package is concluded with two stop bits ('1'). Each data packet thus has 11 bits ; the data rate is 27 bytes per second.

The data packets are transmitted in blocks, whereby the block length must be at least 5 seconds. The structure and size of the blocks is not specified.

1200 baud variant

The company Acorn Computers Ltd implemented a 1200 baud variant in their BBC Micro and Acorn Electron , which reduces the coding of the '0' to a complete wave of the sinusoid with 1200 Hz and the '1' to 2 waves of the sinusoid with 2400 Hz. This extension provides exactly one start bit '0', eight data bits and one stop bit '1'; the result is a data rate of 120 bytes per second (1200 / (1 + 8 + 1)).

The extension stipulates a block length of 256 bytes including consecutive numbering; there must be a time gap with a 2400 Hz tone (carrier) between the blocks. In the event of a read error, this enables you to rewind to a block before the incorrectly read.

Computers supported by the Kansas City Standard

Early micro-computers (some with S-100 bus ):

Home / Personal Computer:

Programmable calculators:

  • Casio
    • FX-501P / FX-502P (with Casio FA-1 interface)
    • FX-602P
    • FX-702P
    • PB700 (with Casio FA-11 interface)

Other variants of the Kansas City standard

The TI-99/4 and TI-99 / 4A home computers from Texas Instruments had the following recording format, which was slow but rather robust in terms of interference:

Audio example of a TI-BASIC file

It started with the pre-tone, consisting of 768 bytes 0x00, followed by a byte 0xFF. Then the byte with the length specification followed twice. The byte designates the number of subsequent 64-byte blocks. At least 0x01 for 1 block, i.e. 64 bytes. Maximum 0xFF for 255 blocks, i.e. 16320 bytes. 0x00 as a length specification is not permitted. The pulsing sound that followed was created by dividing the data to be saved into blocks of exactly 64 bytes each. Each block was preceded by 8 bytes 0x00 followed by 1 byte 0xFF for synchronization. To ensure data security, each block received a checksum byte at the end. This structure, which is 74 bytes long, was also always written twice. To read in again, the timer in the TMS9901 I / O chip measured the length of the half-waves of the audio signal. A long half-wave meant a zero. Two short half-waves stood for a one.

The typical "TI sound" resulting from all of this was familiar to every user and even made it into a television series. The author of the book Programs for the TI-99 / 4A (Hofacker, 1983) Rainer Heigenmoser worked as a technical consultant in the German-language television series Der Bastard (1989). A fax machine is shown at one point. However, the sound played during the fax transmission does not come from a fax transmission, but from a TI-99 / 4A that is stored on a cassette.

See also

  • UEF - a common file format for storing data in the Kansas City standard.
  • Datasette

Individual evidence

  1. ^ Virginia Peschke: BYTE's Audio Cassette Standards Symposium . In: BYTE Publications (Ed.): BYTE . 1, No. 6, February 1976, pp. 72-73.
  2. ↑ David Bunnell : BYTE Sponsors ACR Standards Meeting Archived from the original on September 27, 2007. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: Altair Users Group, MITS Inc. (Ed.): Computer Notes . 1, No. 6, December 1975, p. 1. Retrieved May 4, 2007. @1@ 2Template: Webachiv / IABot / www.startupgallery.org
  3. ↑ see Michael Holley's homepage
  4. ^ Don Lancaster : Build the Bit Boffer . In: BYTE Publications (Ed.): BYTE . 1, No. 7, March 1976, pp. 30-39.
  5. ^ Harold A. Mauch: Digital Data on Cassette Recorders . In: BYTE Publications (Ed.): BYTE . 1, No. 7, March 1976, pp. 40-45.
  6. ↑ see table of contents