Is using legacy mode instead of UEFI mode a bad thing to do?
Can using legacy mode instead of UEFI mode affect my laptop in any way?
Solution 1:
It won't cause any damage.
Legacy mode (a.k.a. BIOS mode, CSM boot) matters only when the operating system boots. Once it boots, it doesn't matter anymore. If everything works as expected and you're happy with it, legacy mode is fine.
Advantages of UEFI boot include:
- Faster boot times. UEFI can skip initialization of some devices which would be reinitialized by OS anyway
- Optional extra security. You can enable Secure Boot, which checks digital signatures of OS components, ensuring that they weren't tampered with. You should combine it with BIOS password protection.
- If you're using multiple OSes, UEFI offers boot manager integrated into firmware.
- If you're using Windows, UEFI mode lets you use GPT partitioning scheme, which supports disks over 3 TB. (Linux can use GPT without UEFI)
Solution 2:
Is it bad? Not at all. Switching to legacy mode might confuse or break a bootloader that expects UEFI, but you can always switch back if you aren't able to boot. Nothing will be permanently changed. You will, of course, lose UEFI-specific features like Secure Boot.
Original BIOSes were quite simple. They initialized hardware, set up BIOS functions that could be called while in real (or VM86) mode, copied the first sector from the primary storage device, the MBR, to address 0x7C00 and executed it. The BIOS itself remained in the first page of memory where it held components (such as the IVT and BDA) that were needed if returning to real mode.
Modern UEFI systems are significantly more complex and do a lot more under the hood. However, some operating systems expect BIOS behavior and won't work with UEFI. The solution is CSM mode, or legacy mode, where a UEFI module is loaded that exposes itself to the operating system like a genuine BIOS, allowing compatibility with systems that require legacy BIOS features.
The operating system doesn't need to be aware of UEFI-specific behavior the firmware is running in CSM mode. See OSDev's page on UEFI for more information.