Reading an Amiga-formatted disk with a single PC disk drive is only partially possible. Here's how it works: 1. The minimum amount of data that must be written to a PC disk so that the FDC can re-read the track When formatting a full track on a PC, here's what the FDC does (source: "8088 et ses p‚riph‚riques, les circuits cl‚s des IBM PC et compatibles" by H. Lilen, edited by ditions Radio): Wait for the index pulse, then write sequentially: 80 bytes with a value of 0x4E (Gap 4A) 12 bytes with a value of 0 (Sync) 3 bytes with a non-MFM value of 0xC2 (Sync) 1 byte with a value of 0xFC (Index Address Mark) 50 bytes with a value of 0x4E (Gap 1) 12 bytes with a value of 0 (Sync) 3 bytes with a non-MFM value of 0xA1 (Sync) 1 byte with a value of 0xFE (ID Address Mark) 4 bytes (sector ID data: track number, head number, sector number, bytes/sector) 2 bytes (sector ID CRC) 22 bytes with a value of 0x4E (Gap 2) 12 bytes with a value of 0 (Sync) 3 bytes with a non-MFM value of 0xA1 (Sync) 1 byte with a value of 0xFB (Data Address Mark) ----- =206 bytes these bytes are followed by 512 bytes of sector data, then other sectors, separated by a Gap 3, and finally a last gap until the next index pulse. It is possible to reset the FDC roughly when the first byte of sector data is transferred. To do so, the last byte of sector ID data (bytes/sector) must have been transfered (DMA counter reaches the value 4), then wait for the right time to execute a reset roughly on the first byte of sector data. When the FDC is reset, it stops formatting the track, so only about 207 bytes are actually written on the track. Other data are kept unchanged. With these 206 bytes written, it is now possible to read the entire track by reading the written sector with a track size specified at 8192 bytes at least. Since all IDs and syncs for this sector are present on the track, the FDC can read what was previously present on the disk. If it was an Amiga-formatted disk, you read what remains, that is more than 98% of the Amiga track! It is also possible to write the following "unnecessary" pre-gap with a higher density: 80 bytes with a value of 0x4E (Gap 4A) 12 bytes with a value of 0 (Sync) 3 bytes with a non-MFM value of 0xA1 (Sync) 1 byte with a value of 0xFC (Index Address Mark) 50 bytes with a value of 0x4E (Gap 1) ----- =146 bytes, that are 73 bytes with a 500 Kbits/sec. rate (high-density), and 37 bytes with a 1 Mbits/sec. rate (extra-high-density). The remaining information (first sector header) of 60 bytes cannot be written with a higher bit rate since the controller must be able to read it in low density. So that leaves 73+60=133 bytes to be written with an AT controller (97 bytes with an EHD controller). 2. The way the Amiga writes a track Unfortunately, the Amiga writes a track WITHOUT waiting for an index pulse. Since the PC waits for an index pulse, the 133 or 97 bytes necessary to be able to re-read the track on a PC are written anywhere on the Amiga track. As a result, up to two Amiga sectors can be altered in a way that is not recoverable. No sector is altered if bytes are written on the track gap of an Amiga track. One sector is altered if bytes are written on the data of an Amiga sector, and two sectors are altered if bytes are written on the end of the data of a sector and on the header and beginning of the data of the following sector. 3. Conclusion Securely reading an Amiga disk with a single PC disk drive attached to a standard PC controller is unfortunately impossible because of the different index synchronizations. I hope it is now proven that nobody will ever be able to do it.