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So I am creating a custom bootloader:

nasm -f bin boot.asm -o boot.bin

It is 512 bytes. How do I place this into a floppy image and boot with qemu?

I tried:

dd if=boot.bin of=floppy.img bs=512 count=2880
dd if=floppy.img of=floppy2.img bs=512 count=1
qemu-system-i386 -fda floppy2.img

But the floppy2.img gets resized to 512 bytes instead of the normal size of 1.44MB. Is this the correct way? I would rather not use any fancy tools, if it can be done with dd, that would be great.

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If the only problem is that the image file is too short, you could try appending 2879*512 zero bytes to the floppy.imgfile:

dd if=/dev/zero count=2879 bs=512 >> floppy.img

On the other hand, if you need to store somthing else than just the boot sector on the floppy image, you will have to create a FAT file system on it. The way to do this is to use a loop device.

sudo losetup /dev/loop0 floppy.img
sudo mkfs -t fat /dev/loop0
sudo mount /dev/loop0 somedir

where somedir is an empty directory where /dev/loop0 is mounted. You can now copy the needed files to this directory.

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