Explain boot windows XP from a USB flash disk.

trying to understand in depth booting Windows XP but I do not know. I read a lot of topic but everywhere is the only code and no explanation how it worked.

 

I modified code (only deleted lines ) from Easy2Boot from steve6375. thx .

 

title XP Step 1

#In this case, does not matter FIRA settings
set FIRA = 3

call /_iso/e2b/grub/DPMS/dpms2.g4b 2

# map -- mem /newwinvblock.ima.gz (fd0)
# map -- mem /newwinvblock.ima.gz (fd1)

map /winXP.iso (0xff)
map (hd0) (hd1)
map (hd1) (hd0)
map --e820cycles=3
map --hook
root (0xff)
chainloader (0xff) /i386/setupldr.bin | | chainloader (0xff)

I understand that in dpms2.g4b is set driver for hdd and firadisk (winvblock) to (fd0) (fd1) drive. But I do not understand how to activate firadisk (winvblock) when installing windows without any text file as autounatend.xml for win7 .

 

 

And next code.

title XP Step 2
map --mem /newwinvblock.ima.gz (fd0)
map /winXP.iso (0xff)
map (hd0) (hd1)
map (hd1) (hd0)
map --hook
map --rd-size = 2048
map --mem (rd) +4 (0x55)
map --rehook
write (0x55) #!GRUB4DOS\x00v=1\x00/winXP.iso\x00\xA0\x00
root (hd0,0) || root (hd0,1) || rootnoverify (hd0,0)
chainloader (hd0) +1

And here's when and how to activate winvblock ? Or how is it possible that the installation works?

 

And the last question, why you need map newwinvblock.ima.gz to (fd0) drive and (fd1)?

 

Can someone explain to me, please ?

 

Thank for some reply.