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I simply made a following bootloader

jmp $
times 510 - ($ - $$) db 0
db 0x55
db 0xaa

then I did following 

nasm bootloader.asm -o bootloader

dd if=bootloader of=/dev/sdb bs=512 count=1

I tested on 2 computers. I set usb hdd as highest boot priority for both computer.

Old computer with Intel Pentium M process (lenovo) boot with the bootloader from usb drive

but Newer computer with Intel i5 process(lenovo) says that there's no operating system.

(if there's hdd on boot sequence, the usb led blinks several times and the computer boot from hdd drive. if there's no hdd on boot sequence, An error Operating System Missing occurs)

I opened a ubuntu utility called 'Bless' as super user and check /dev/sdb

indeed there is 0x55 0xaa at the 0x1fe and 0x1ff respectively.

I have no idea why I can't boot with it on some computer.

both computer has same UEFI setting, boot priority, no password.

please help

Taeyun
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1 Answers1

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Some BIOS require that you add the BPB standard code to easily identify the the USB and its filesystem.

You can add this to the start of your code to be identified with all BIOS. And Most of them with load it properly.

Adding this works for all types of media. Floppy as well as HDD, USB, etc.
This will add a recognised FAT12 file system to your drive as well.
Check out osdev wiki.

;bits   16                      ; we are in 16 bit real mode
use16
org     0                   ; we will set regisers later

start:  jmp main                    ; jump to start of bootloader
;nop                ; Pad out before disk description

; ------------------------------------------------------------------
; Disk description table, to make it a valid floppy
; Note: some of these values are hard-coded in the source!
; Values are those used by IBM for 1.44 MB, 3.5" diskette

bpbOEM          db "My OS   " ; Disk label
bpbBytesPerSector:      DW 512 ; Bytes per sector
bpbSectorsPerCluster:   DB 1 ; Sectors per cluster
bpbReservedSectors:     DW 1 ; Reserved sectors for boot record
bpbNumberOfFATs:    DB 2 ; Number of copies of the FAT
bpbRootEntries:     DW 224 ; Number of entries in root dir
; (224 * 32 = 7168 = 14 sectors to read)
bpbTotalSectors:    DW 2880 ; Number of logical sectors
bpbMedia:       DB 0xf0  ;; 0xF1 ; Medium descriptor byte
bpbSectorsPerFAT:   DW 9 ; Sectors per FAT
bpbSectorsPerTrack:     DW 18 ; Sectors per track (36/cylinder)
bpbHeadsPerCylinder:    DW 2 ; Number of sides/heads
bpbHiddenSectors:   DD 0 ; Number of hidden sectors
bpbTotalSectorsBig:     DD 0 ; Number of LBA sectors
bsDriveNumber:          DB 0 ; Drive No: 0
bsUnused:       DB 0
bsExtBootSignature:     DB 0x29;0x41 ; Drive signature: 41 for floppy
bsSerialNumber:         DD 0xa0a1a2a3 ; Volume ID: any number
bsVolumeLabel:          DB "MOS FLOPPY " ; Volume Label: any 11 chars
bsFileSystem:           DB "FAT12   " ; File system type: don't change!

maincode:

jmp $
times 510 - ($ - $$) db 0
db 0x55
db 0xaa

Compile it as usual with nasm. And set it as MBR with dd.

Divyavrat
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