07-28-2017, 12:52 PM
[member=540]Monkeyman[/member],
My understanding is as follows...
The Legacy BIOS (aka CSM or compatibility support module) vs UEFI divide actually encompasses two concepts:
- disk partitioning
- booting an operating system
UEFI firmware will only handle disks with GPT partitioning, while Legacy BIOS can generally use either MBR or GPT partitioning. UEFI also insists on certain information and software being on a disk in a specific partition (known as the System partition or ESP) to use for booting an OS (i.e. the primary OS boot loader). UEFI also introduces the concept of signed components used for the boot process: Secure Boot. While most UEFI firmware still supports disabling secure boot, it is unclear how long this will continue.
Regarding switching between CSM and UEFI booting: this can be feasible if a disk is carefully GPT partitioned, however the two modes require different O/S boot loader (e.g. GRUB) configurations so switching is not necessarily easy or trivial. It is probably easier to make the switch with open source OSes than proprietary ones though, and some boot loaders (e.g. GRUB) can be used for either mode when appropriately configured. Also, at some point Microsoft is likely to stop supporting installing Windows in Legacy mode which may affect your choice.
Advantages of UEFI:
- UEFI has its own shell and can store user-supplied information in non-volatile memory
- UEFI firmware can be 32 or 64 bit natively, escaping some of the limits of the primary boot loader in the Legacy BIOS which still has 16 bit code in the boot phase
- UEFI booting tends to be faster than Legacy booting, because of the removal of 16 bit BIOS routines from the process
There are other advantages to be gained from using GPT disk partitioning rather than MBR (also aka Legacy) partitioning:
- support for partitions > 2.2TB
- support for up to 127 primary partitions
If your motherboard or system's firmware easily allows selection of the mode and you don't need the increased partition size or number of partitions for GPT, it currently doesn't matter which you choose if you can install the OSes you're interested in.
I have succeeded with installing LL 3.4 in a UEFI boot environment on an Intel NUC which supported both modes, guided by m654321's tutorial, so it is possible but it was time consuming. Unfortunately a lot of newer laptops, especially less expensive models, are dispensing with CSM support so figuring out the UEFI installation situation will become more important as time goes on.
My understanding is as follows...
The Legacy BIOS (aka CSM or compatibility support module) vs UEFI divide actually encompasses two concepts:
- disk partitioning
- booting an operating system
UEFI firmware will only handle disks with GPT partitioning, while Legacy BIOS can generally use either MBR or GPT partitioning. UEFI also insists on certain information and software being on a disk in a specific partition (known as the System partition or ESP) to use for booting an OS (i.e. the primary OS boot loader). UEFI also introduces the concept of signed components used for the boot process: Secure Boot. While most UEFI firmware still supports disabling secure boot, it is unclear how long this will continue.
Regarding switching between CSM and UEFI booting: this can be feasible if a disk is carefully GPT partitioned, however the two modes require different O/S boot loader (e.g. GRUB) configurations so switching is not necessarily easy or trivial. It is probably easier to make the switch with open source OSes than proprietary ones though, and some boot loaders (e.g. GRUB) can be used for either mode when appropriately configured. Also, at some point Microsoft is likely to stop supporting installing Windows in Legacy mode which may affect your choice.
Advantages of UEFI:
- UEFI has its own shell and can store user-supplied information in non-volatile memory
- UEFI firmware can be 32 or 64 bit natively, escaping some of the limits of the primary boot loader in the Legacy BIOS which still has 16 bit code in the boot phase
- UEFI booting tends to be faster than Legacy booting, because of the removal of 16 bit BIOS routines from the process
There are other advantages to be gained from using GPT disk partitioning rather than MBR (also aka Legacy) partitioning:
- support for partitions > 2.2TB
- support for up to 127 primary partitions
If your motherboard or system's firmware easily allows selection of the mode and you don't need the increased partition size or number of partitions for GPT, it currently doesn't matter which you choose if you can install the OSes you're interested in.
I have succeeded with installing LL 3.4 in a UEFI boot environment on an Intel NUC which supported both modes, guided by m654321's tutorial, so it is possible but it was time consuming. Unfortunately a lot of newer laptops, especially less expensive models, are dispensing with CSM support so figuring out the UEFI installation situation will become more important as time goes on.