Yes the majority of that deals with writing to a FAT filesystem. However, it shows the general structure of the boot sector before any file operations. The code for the menuetOS that I posted previously for instance, won't load. However this code:
boot_program equ 07c00h ;position for boot code
jmp start_program
nop
oemname db 'MENUETOS'
bytespersector dw 512
sectorspercluster db 1
ressectors dw 1
numcopiesfat db 2
maxallocrootdir dw 224
maxsectors dw 2880 ;for 1.44 mbytes disk
mediadescriptor db 0f0h ;fd = 2 sides 18 sectors
sectorsperfat dw 9
sectorspertrack dw 18
heads dw 2
hiddensectors dd 0
hugesectors dd 0 ;if sectors > 65536
drivenumber db 0
db 0
bootsignature db 029h ;extended boot signature
volumeid dd 0
volumelabel db 'MENUET DISK'
filesystemtype db 'FAT12 '
start_program:
xor ax,ax
mov ss,ax
mov sp,boot_program
push ss
pop ds
mov si,loading+boot_program
loop_loading:
lodsb
or al,al
jz procura_arquivo_novamente
mov ah,0eh
mov bx,07h
int 010h
jmp loop_loading
procura_arquivo_novamente:
push ss
pop es
mov bp,16
newtry:
dec bp
loop_envio_mensagem:
lodsb
or al,al
jz espera_digitar_tecla
mov ah,0eh
mov bx,07h
int 010h
jmp loop_envio_mensagem
espera_digitar_tecla:
jmp $
loading db 13,10,'Starting MenuetOS ',00h
times 0x1fe-$ db 00h
db 55h,0aah ;boot signature
With the relevant declarations of bytes and words at the beginning does launch successfully. So I'm figuring that snippet of code is what makes all the difference. As the author of the link that I stated he shows that the boot sector can be divided into 6 areas:
Assembly Language Jump to Boot Code
Disk Parameters Needed by DOS
Assembly Language Boot Code
Error Messages
System File Names
DOS Signature
The DOS Signature refers to the 'magic number' 55aah, the Assembly Language Jump to Boot Code is a DOS requirement according to the author along with a NOP after it, precisely as the menuetOS author is doing. The Disk Paramters Needed by DOS are those that the menuetOS author has included on his code, finally the actual boot strapper code is located in Assembly Language Boot Code, the Error Messages and System File Names are also part of that if I'm not mistaken but are this FAT system specific code of the author.