Mov ah, 0x02 read sectors into memory (int 0x13, ah = 0x02) Reads sectors from disk into memory using BIOS services Jmp _stage2 start execude instructions of _stage2 Mov bx, print data at _stage2data to confirm stage 2 was loaded Jnc execute_stage2 if carry flag is set, disk read failed Mov bx, 0x7E00 destination, right after your bootloader Mov ax, 0x7C0 set DS to 0x7c0 so pointing at 0x0 resolves to 0x7C0:x0000 = 0x7C00Ĭld set direction flag to make string operations count forward Mov sp, 0x7C00 right before MBR, counting upwards It looks to me like the stage2 load fails silently (error branch doesn't get called) and i am looking to solve this for two weeks now without success.

This works fine in QEMU but fails in virtualbox and on hardware. I confirmed with a hex editor that the size of final binary 'program.bin' is exactly 1024 byte long and contains both 'signatures' (last two bytes of each stage, 0xAA55 for stage1 (MBR signature) and 0xCC77 for stage2).Įxpected outputs are: 1 // stage1 started Stage1 then proceeds to load stage2 from the drive and jumps to it.

stage 1 gets loaded by the bios into the MBR area. My bootloader consists of two 512 byte stages.

Virtualbox boot from usb