EncodingData and Clock are recorded in separate tracks at 9600 bits per second. No modulation is used, data is written in base binary format at TTL levels.
The 9.6 KHz clock is utilized to encode and decode bits by the mean of a UART chip 16C550. The byte format (programmed in the chip) is: 8 data bits, 1 stop bit, no parity.
Data is expected to be grouped into blocks separated by gaps. The length of a block is determined by the software making use of the drive, expected in the order of one to a few kilobytes.
Gaps are defined in the clock track. Within gap areas, the clock is 1.2 KHz instead of 9.6 KHz. No-file areas (for example, all tape long after the last block) is distinguible because of the absence of pulses in the clock track.
The use of separate tracks for clock and data and the non use of modulation presents the following advantages:
* High tolerance to variations in tape speed (Wow and flutter)
* About ten times the bit rate as compared to modulated encoding.
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