Minor change
I got tired of having to untick 'No user prompts' when I wanted to install grub4dos to the MBR and then install grub4dos again to the PBR. Now if you have 'No user prompts' ticked, it will prompt for MBR or PBR, but there are no more prompts after that.
I got tired of having to untick 'No user prompts' when I wanted to install grub4dos to the MBR and then install grub4dos again to the PBR. Now if you have 'No user prompts' ticked, it will prompt for MBR or PBR, but there are no more prompts after that.
Is there every a time it is beneficial to only install to either MBR or PBR ONLY? I always install to both
ReplyDeleteNormal booting involves loading the code from the MBR into memory and running it.
ReplyDeleteThe grub4dos stage 1 code in the MBR loads grldr (grub4dos) - it does not read the code in the PBR at all.
However, it has been observed that some BIOSes look to see what partition is marked as the Active (boot) partition and then load the sector at the PBR into memory and run that code - the MBR code is never run by these BIOSes!
You could always just install grub4dos to the PBR, however with a standard BIOS, this relies on the code in the MBR being the standard code which will load the PBR code. If it is not standard code or if there is a problem with the BIOS and CHS translation, then the MBR - PBR - grldr boot chain might fail.
So neither installing just to MBR or installing just to PBR is perfect. I used to think that installing to MBR was best because the boot chain (MBR - grldr) was more direct, however these non-standard BIOSes have appeared which seem to boot the PBR directly.
So if you had to choose just one, I would now say choose PBR.
For E2B use, installing to both is the best option as that way you know what code is in the MBR and PBR and you know that either BIOS type should work.
Also, RMPrepUSB uses a modified/recompiled version of grubinst.exe code for the MBR to make it even more compatible (the start bytes have been changed as a problem with some BIOSes was found with the standard version).
For this reason, if you use the *standard* version of grubinst.exe to install grub4dos, it is best to choose just PBR (unless you want to install grub4dos on an exFAT filesystem in which case you have to use MBR).
If using RMPrepUSB, installing both gives the best of both worlds and maximises the chances of booting.
Thanks for taking the time to reply in such detail! I've learned something :-D Cheers
ReplyDelete