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I made my own DOS implementation (Announce)

posted by bretjohn Homepage E-mail, Rio Rancho, NM, 17.12.2025, 21:47

> The boot sector signature is only required for hard disks. Bootable
> floppies don't need it.
This can be very confusing. The word-sized signature at the end of a 512-byte sector (be it a Master Boot Record or Volume Boot Record) indicates an IBM-compatible boot sector. It doesn't mean the sector will actually boot anything, but it means it should be safe to execute it as if it will load an OS (i.e., it shouldn't crash). Booting mechanisms will also (or sometimes only) look at the first several bytes of the sector to see if it looks like executable code (usually, the first byte is a JMP OpCode).

You also need to be careful when you use the term "floppy" since hard drives (including bootable ones and removable ones) can be configured as a "superfloppy" where they just have a BPB/VBR and don't have an MBR (and only have one "partition").

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