Restoring the Hitachi FW: The 4 bytes difference

After playing around a bit with the Xtreme FW for the Hitachi 47D in my 360 I deceided to flash the FW back to it's original state. After using the SlaxVM-solution to put the drive in ModeB I used the restore.bat included with the Xtreme-package. No problems during the flashing-process, so I thought I was good to go.

I deceided to dump the new flashed FW to compare it against the FW-dump made before I flashed the Xtreme-FW. I didn't expect to find any differences: however there were! Using the fc (filecompare) command I found out 4 bytes were different between the two dumps:

0003E7FC: B6 00 (B6 = "original", 00 = "restored")
0003E7FD: 1C 00
0003E7FE: 68 00
0003E7FF: 33 00

Hmmm, I wanted to restore the FW to the original-state, not to the "almost" original-state. A quick look at the restore.bat file included in the Xtreme FW-package shows me the reason for not flashing back to the entire original situation. The very first flash-command was made a remark:

rem @echo Flashing sector 9003e000 (Master Checksum)...

Uncommenting the above line by removing the "rem" would be the solution to flash back the entire original FW. However the question remains (at least for me) why the 4 byte difference, and more: what do these 4 bytes do/mean?

So I went over to xboxhacker.net to see if my questions had been answered before. And as expected: They were :) Thanks to Garyopa at the xboxhacker BBS I learned what the 4 bytes indicated as "Master Checksum" were and why they were not flashed back:

"The reason the Master Checksum is not flashed back, is because incase one of the other restore flashes failed, or the backup was corrupt or a byte got changed somehow, and the user turned the power off, before checking all the flashes were OK, and the backup was 100% correct, the drive would be a BRICKed drive if the checksum does not match. "

My suggestion is for those of you who want to flash back the entire FW to alter the restore.bat from the Xtreme-package and move the line "@echo Flashing sector 9003e000 (Master Checksum)" to the end of the flashing process. Obviously don't forget to remove the "rem" at the begin of the line. By moving the flash of the "Master Checksum" to the end of the bat-file the checksum will not be set when one of the earlier sector flashes fail (and the batch-file gets aborted by the user!).