7.1.6) What is the Atari cassette utilization/filesystem?

(Section sources include: De Re Atari, OS Users Manual, XL Addendum)

The following are characteristics of the cassette utilization/filesystem
as implemented by the Atari Operating System.

- Mark = 5327Hz (audible sound frequency)
- Space = 3995Hz (audible sound frequency)
- Bit = space(0) or mark(1)
- Byte = 10 bits:
    - 1 start bit (space)
    - 8 data bits
    - 1 stop bit (mark)
- Record = 6-132 bytes, as follows:
    - Speed measurement byte, first of two.  Marker character = $55 (hex)
    - Speed measurement byte, second of two.  Marker character = $55 (hex)
    - Control byte.  One of three values:
       1) $FC = Record is a full data record.
       2) $FA = Record is a partially full data record, and the next record
                should be an end-of-file record.
       3) $FE = Record is an end-of-file record.
    - Data bytes.  128 bytes for a full data record or an end-of-file record,
      or 2-128 bytes if a partially full data record, where the last byte is
      not really a data byte, but rather contains the number of actual data
      bytes (1-127).
    - Checksum byte
- Pre-Record Write Tone (PRWT) = pure mark tone
- Post-Record Gap (PRG)
- Record Frame = PRWT + Record + PRG
- Inter-Record Gap (IRG) = PRG + PRWT
- Normal IRG Mode: Tape comes to stop after each record frame
- Short IRG Mode: Tape is not stopped between record frames. 
   (Short IRG Mode is supported by the Atari BASIC commands CSAVE and CLOAD.)
- Normal IRG PRWT = 3 seconds of mark tone
- Short IRG PRWT = 0.25 second of mark tone
- Normal IRG PRG = Up to 1 second of unknown tones (motor stop/start time)
- Short IRG PRG = pure mark tone, duration set by user program (may be zero)
- File consists of:
    1) 20-second leader of mark tone
    2) Any number of data record frames (each frame contains one data record)
    3) End-Of-File record frame (contains an end-of-file record)
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