Older PCs have BIOS that uses MBR on the storage media for information for access. Modern systems have UEFI that uses GUID with GPT partitions on the storage media for access.
If you have an old system with a new boot disk with a GUID partition, you may not be able to boot or worse, it will freeze the PC at POST.
You can use the GDisk software to manipulate the partition to include the necessary boot information for your BIOS or UEFI systems.
When I installed my copy of FreeNAS on a USB stick, my old computer with a Abit AW9D-MAX refused to boot as it does not recognize the GUID partition. Using GDISK solved my problems but I needed my Mac with a way to determine the device number which is recognized by MacOS.
I used gdisk (http://www.rodsbooks.com/gdisk/gdisk.html) to create a hybrid MBR:
- Run gdisk (sudo gdisk)
- Select the FreeNAS boot USB (/dev/disk4)
- Type ‘r’ to enter Recovery menu
- Type ‘h’ to create the Hybrid MBR
- Follow the prompts. For me, I selected partition 2, and choose all the default options thereafter. Please read the info at the link above and be sure you’re not doing something to destroy data!
- When you’re done, type ‘w’ to commit your changes.
Good to know these tricks!