However, to put the A1 out of sync, the following pattern is produced by the clocking bits : 0 0 0 1 0 1 0. A1 should be encoded as data bits 100010010101001 and clocking bits 0 0 0 1 1 1 0 and is encoded that way in a Sector Data field (there is no reason for it to appear in a Sector ID field). The A1 in the Sync bytes does not follow the appropriate clock and data bit pattern.
However, with this limitation is more liberal than how the bits are actually represented in MFM. In MFM encoding, there will never be more than three 0 bits between a 1 bit. But there is one time when they intentionally are not, the Sync bytes. Normally the two are in sync, meaning that the clock bits correspond exactly to the MFM data bits. There are two data bits for every clock bit. Both are present on the Write Data and Read Data lines. There is a relationship between the MFM clock bits and the MFM data bits. The data line of a floppy disk does not operate in a vacuum.
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