Additional note: MBR and GPT are partition tables. MBR has severe limitations.
Legacy (aka “BIOS”) boot process loads first stage of bootloader from sector 0 of a disk. IIRC, the disk can have either MBR or GPT. (GPT does not have data within sector 0, like MBR, but GPT can have a “protective MBR” data in sector 0.)
EFI boot process seeks bootloader binaries from EFI System Partition (ESP, a fat32 filesystem). Only GPT can have ESP.
One can also boot in legacy mode from small MBR system disk and have large GPT disks for data.
Thanks for the information. I have put it in my “Tool Box” for future reference. I have been trying to AVOID at all cost anything that has to do with Microsoft. As I once said, I am “Old School”: My largest disk is a 2 TB HDD that serves only for Backup. My other 2 drives are a 1 TB NVMe 4.0 drive that holds my NEW Rocky Linux 8.4 Conversion; and a 1 TB 2.5" SSD that is probably going to hold openSUSE 15.3
jlehtone you have always proved to be a source of invaluable information – ALWAYS!! As you have correctly pointed out Legacy BIOS is limited to disks to s size no more than 2 TB – once a unimaginable size. Here however, is where the practicable meets theory: I live on SSD, I can not afford to buy drives much in excess of 2 TB: 2TB NvMe 4.0 drives are cost prohibitive; likewise 4 TB 2.5" SSD’s are to costly. The only drives in excess of 2TB is HDD spinning rust. You can get some whopping good deals on HDD. Yet the ONLY thing I use HDD’s for is BACKUP STORAGE.
Truthfully, I don’t know the difference between Secure Boot, UEFI, /boot/efi, and GPT. Rightly or wrongly I have lumped them all together as “Microsoft Specifications”. I might, for example, be willing to use /boot/efi so long as the rest of my legacy setup and equipment does not have to convert to either UEFI and / or Secure Boot.
Again THANK YOU for your wise words, I just hope you understand my situation. This is a small workstation. It was built with parts “ON SALE” … with the exception of the CPU. I still paid less than $2,000 for an AMD Ryzen 9 5900X based system with 64 GB of GSkill Trident Z Neo RAM on an ASUS Prime X570 Pro Motherboard. It took between 1.5 and 2 years to buy all the parts – I’d buy a part and squirrel it away; I’d buy a part and squirrel it away. i’d hate to know what Dell or HP would charge for such a system. Indeed if you bought an equivalent system you know that it would be built with bargain basement parts. Life on SS can suck big time, but you would be amazed what you can do on limited funds if you make a plan and carry out the plan.
I wouldn’t sweat the details too much, tbh. While it’s good to know how it all works together the important thing is that none of it matters for converting from CentOS 8 to RockyLinux except for SecureBoot and migrate2rocky will tell you if that’s an issue.
As far as all the rest of it goes, RockyLinux will work just fine with legacy bios, or EFI, or whatever you happen to have. The only limitation is the 2TB one that has already been discussed. Since that’s not an issue for you (at least for now) then there’s no need to worry over it. Presumably there will come a time when that does become an issue, because disk (and SSD) sizes increase and price goes down over time, but you can certainly wait until then to cross that bridge.