In grub4dos, the so-called "continuity" of a file means that the physical storage location of this file on the disk is a continuous sequence of sectors without "holes". Or in plain language, a "continuous" file is a "non-fragmented" file.
The files created by the operating system are not necessarily continuous. A file may be divided into many fragments. The contig and wincontig commands can organize a discontinuous file into a continuous one. I have used the contig command, but it may not be completed at one go, and may need to be organized multiple times before it can finally become a continuous, non-fragmented file.
The map command can detect whether a file is continuous. For a discontinuous file, the map refuses to simulate it. But in the case of map --mem, the file does not need to be continuous, because at this time map will copy each fragment of the discontinuous image file to memory and become a continuous image file (in memory).
Since the simulation code of map uses the BIOS of the motherboard instead of DOS, the ordinary discontinuous files that can be accessed under DOS cannot be accessed in the eyes of the simulation code of map. The BIOS only recognizes the concept of "sector" and does not recognize the concept of "file". And the simulation code only uses the BIOS, so it does not recognize DOS files. However, when a DOS file is organized into a continuous one, it becomes a continuous sequence of "sectors", so the simulation code can then access it conveniently. In principle, the simulation code can also be designed to support image files with multiple fragments, but this requires a lot of work, is more complicated to handle, and is difficult to implement.
grub4dos currently supports the simulation of floppy disks, hard disks, and optical disks. The latest memdisk also supports these simulations. ISO simulation means using an ISO file to simulate an optical disk.
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