In figure 5 you can also see the different SYNC's 12 times of 00h. You also need an „Option Board“ for overwriting the bytes „between“ the DATA areas! You can NOT do this writing with a normal HEX editor. The special thing about GRAPH 2 is that I used the „Deluxe Option Board Transition Editor (TE)“ to overwrite the whole area of sector 5 from address mark A1A1A1FE with the character „D“ without exception every byte! Of course the floppy is now defective! I did this to see the exact beginning and end of the sector. In figure 5 you can see two GRAPH's placed one on top of the other. Only in this area, the data/information itself is stored under DOS. Of particular importance is the DATA sector (yellow) of 512 bytes. If the byte sequence is A1A1A1 FB, then it is the data address mark (DAM) and the actual data area of 512 bytes follows immediately. If the byte sequence is A1A1A1 FE, then it is the ID address mark (IDAM) and the ID with the CHSB information (4 bytes: Cylinder, Head, Sector, Bytes/Sector) follows. They start after SYNC 2 or 3 with 3 times A1h followed by a FEh or FBh. In each sector there are always two characteristic address marks (AM). Finally a track is completed by the GAP 4B field. Then follows the repetition of ID FIELD and DATA FIELD. The first is the INDEX FIELD field, which appears only once at the beginning of a track. The figure can be roughly divided into three parts. 3: Sector 3 filled with letter „A“įigure 4 shows the scheme for the standard IBM MFM format of a floppy track. In order to locate an exact DATA area (see figure 1), I manually wrote the character „A“ exactly 512 times into the DATA sector 3 with a normal HEX editor. Then I formatted this disk on a true 360K floppy disk drive (TEAC FD-55BR) with DOS (DS, DD/MFM, 9 sectors, 40 tracks, 512 bytes/sector). You can see the result of the data flow in figure 1. In all figures you always see the first track of the floppy disk, track 0.įirst of all, I picked out a 5.25" (360K) floppy disk that had never been used and was not preformatted. Exploring an IBM standard MFM track of a floppy disk What does an IBM standard MFM track with the KryoFlux look like? The following figures can be created directly with the KryoFlux while reading the RAW stream. ![]() This article is more or less the follow-up to my article on: „Exploring the IBM MFM standard track format“ with the Deluxe Option Board and the „Transition Editor“ (TE).
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