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This error signals to the disk controller that this is a Sync byte.Īnother method is to check that the exact number of Gap and Sync Bytes are on the disk. The resulting fifth bit is not as it should be, instead it appears as 100010010 001001, with the fifth bit being different. 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. ​ Here's how to tell the difference on 5.25" disks.The data line of a floppy disk does not operate in a vacuum. ​ Here's how to tell the difference on 3.5" disks.

When formatted for IBM, the disks are 360K. ​ When used in connection with 5.25 inch floppy disks, the disk are 500K before the disk is formatted. When formatted for IBM, the disks are 720K. ​ When used in connection with 3.5 inch floppy diskettes, the disk capacity is 1MB before the disk is formatted. Sometimes called MF2-DD or low density disks. ​ DS/DD or MF2-DD "low density": ​ The term DS/DD means double sided double density. When formatted for IBM, the disks are 1.2 MB. ​ When used in connection with 5.25 inch floppy disks, the disk capacity is 1.4 MB before the disk is formatted. When formatted for IBM, the disks are 1.44 MB.

​ When used in connection with 3.5 inch floppy diskettes, the disk capacity is 2.0 MB before the disk is formatted. ​ DS/HD or MF2-HD "high density": The term DS/HD means double sided high density. We offer a wide variety of DS/HD and DS/DD floppy disks.