Notes:
* The Index Address Mark (IAM) signifies the beginning of a track on a floppy disk.* The ID Address Mark (IDAM) marks the beginning of a sector's header on a floppy disk.* The Data Address Mark (DATA AM) marks the beginning of the actual data in a sector on the disk.
In MFM (Modified Frequency Modulation) encoding, the IDAM and DATA AM are always preceded by three A1 bytes to help the FDC lock onto the data stream and accurately read the following datas. This is needed because MFM is more compact and harder to read than earlier encoding methods.