What are the differences between UEFI and Legacy BIOS modes on laptops?

1 UEFI Basics

UEFI, the modern replacement for the old BIOS, supports newer computing technologies and has a more user-friendly interface. Unlike BIOS, UEFI stores all its data in an .efi file instead of the firmware, which allows for more robust and flexible pre-boot environments. This means you can use a mouse to navigate through menus, and the system can initialize hardware components and drivers even before the operating system starts. UEFI also supports booting from large hard drives (over 2 TB) and provides a secure boot feature that helps prevent malware from hijacking the boot process.

3 Boot Process

The boot process differs significantly between UEFI and Legacy BIOS. UEFI boots by reading the list of boot loaders from the EFI System Partition (ESP), which is a dedicated partition on your hard drive. This approach is more efficient and flexible, allowing for multiple operating systems without the need for a boot loader like GRUB. In contrast, BIOS uses the MBR to find the boot sector and hand over control to the operating system, which can be less efficient and more prone to errors if the MBR is corrupted.

4 Partitioning Scheme

Partitioning schemes are another area where UEFI and BIOS differ. UEFI uses the GUID Partition Table (GPT), which allows for a virtually unlimited number of partitions and works with disks larger than 2 TB. GPT is more robust and offers better data integrity checks compared to MBR. On the other hand, Legacy BIOS uses the MBR partitioning scheme, which limits the number of primary partitions to four and cannot handle disks larger than 2 TB without additional software or workarounds.

5 Compatibility Mode

To maintain backward compatibility with older hardware and software that may not support UEFI, most modern systems come with a Compatibility Support Module (CSM). CSM allows UEFI-based systems to emulate a Legacy BIOS environment, enabling them to boot older operating systems and interact with older hardware. However, using CSM can sometimes lead to a less efficient boot process and may disable some of UEFI's advanced features.

6 Security Features

Security is a domain where UEFI has a clear advantage over Legacy BIOS. UEFI's secure boot feature prevents unauthorized code from running during the boot process, offering protection against boot-level malware. This feature can be particularly important in preventing rootkits and other sophisticated threats that target the boot sequence. Legacy BIOS does not have a secure boot mechanism, which makes systems using it more vulnerable to certain types of malware.