UEFI vs Legacy BIOS: Firmware Pro Tips for CompTIA A+ Triumph

UEFI (Unified Extensible Firmware Interface) and Legacy BIOS, sometimes referred to as MBR (Master Boot Record), are both BIOS (Basic Input Output System) types which are firmware interfaces that are essential to understand if you are planning to take the CompTIA A+ exam. BIOS is a set of instructions that performs hardware initialization before the operating system boots up. While UEFI has largely replaced Legacy in modern systems, it is still part of the exam curriculum.

First let’s break down what firmware is, it can be understood as the “software for hardware.” It provides essential instructions to hardware devices, enabling them to communicate and function effectively. While firmware and software share similarities in terms of instructions executed by a processor, they serve different purposes and reside in different locations. Firmware is specific to individual hardware components and is stored in read-only memory (ROM), while software runs on an operating system and is stored on storage devices.

UEFI and Legacy represent two distinct firmware interfaces that reside within the motherboard’s firmware chip. Manufacturers embed the BIOS firmware instructions directly into this chip, making them read-only and immutable. A decade ago, when purchasing a motherboard, it would typically come equipped with a legacy BIOS. However, in the present day, almost all new motherboards are shipped with UEFI BIOS.

UEFI and Legacy

The BIOS is the first set of instructions your processor processes when it initially boots. As the acronym suggests, it instructs the computer on how to perform basic input/output functions and load the fundamental computer hardware. Both UEFI and Legacy are types of BIOS, but they differ in how they handle the boot process after the POST (Power-On Self Test) is completed. Legacy BIOS is the predecessor to UEFI, so UEFI inherits many of the fundamental features that legacy BIOS implemented. Let’s first explore the common aspects of the two by going step by step into the boot process.

When a user initiates the boot process by pressing the power button on a computer, the power supply is activated, and it waits until it can provide stable power to the other components. Once sufficient power is available in the PSU, the processor receives power and becomes ready to execute commands. Since the CPU has no instructions in memory, manufacturers pre-program it to search for the BIOS to begin executing instructions to initialize all the hardware.

The initial set of instructions provided by the BIOS to the CPU is known as the POST (Power-On Self Test). During the POST, basic hardware components are checked for any critical issues. The motherboard BIOS then proceeds to look at other devices and executes their BIOS to initialize them. It is important to note that not only the motherboard, but other devices such as video cards and hard drives, may also have read-only memory (ROM) that stores their respective BIOS instructions.

During the system inventory phase, both UEFI and Legacy BIOS conduct thorough checks of critical hardware components, such as memory, storage devices, and peripherals, to verify their proper functioning. If any issues are found during this process, both firmware interfaces display relevant error messages on the screen, making it easier for users to diagnose potential booting problems or hardware-related issues. Additionally, both UEFI and Legacy BIOS take care of configuring various important system settings, such as hard drive parameters and memory timings, in order to optimize the overall performance of the system.

The exact steps and options within the BIOS may differ slightly between different computer systems and BIOS versions. However, the fundamental process described above remains consistent across most modern computer configurations.


As computing continues to advance there were some fundamental flaws of Legacy BIOS that needed to be addressed. To fix these issues the UEFI Forum, a collection of the top hardware companies, collaborated to create UEFI which is a new standardized interface that simplifies secure platform initialization and firmware bootstrap operations. Now, let’s explore the key differences between the two interfaces and understand why the legacy BIOS is being phased out.


In terms of graphical user interfaces (GUIs), the contrast between the legacy BIOS and UEFI BIOS is quite pronounced. The older legacy BIOS offers a basic text-based interface, controlled solely through the keyboard. On the other hand, the new UEFI BIOS provides a visually menu equipped with animations and can be navigated using a mouse. This modern interface not only enhances aesthetics but also offers more comprehensive information regarding the hardware status, keeping users better informed about their system’s operations. UEFI includes the ability to customize the UEFI menu, allowing users to select the information they want to see, change boot settings, adjust hardware configurations, and more.

Partition Drives

Partitions act as distinct sections on a storage drive, each resembling a separate container that houses specific types of data. These partitions are essential because they enable different functionalities and hold separate pieces of the overall system. Partition schemes are pivotal in shaping how data is organized within a filesystem. They determine how a storage drive is divided to facilitate efficient data access by the CPU. In light of the advancements in operating system functionality, their size has grown significantly. Consequently, the effectiveness of the disk partitioning strategy has taken on heightened importance.

Legacy BIOS has a significant drawback due to its limited partition size compatibility. The MBR partitioning scheme that legacy BIOS relies on can effectively handle storage devices only up to 2 terabytes. While this might meet the requirements of typical users, it raises concerns for specialized systems that foresee potential bottlenecks down the line.

Enter UEFI, a significant improvement in this realm. Operating through the GPT partitioning scheme, UEFI blows past these limitations. GPT’s capacity to handle storage devices up to 9 zettabytes exemplifies its far-reaching capabilities. While this immense storage potential remains more of a theoretical benchmark it shows UEFI’s capacity for accommodating the expanding needs of modern computing environments.

Bootloaders / Security

When you download an operating system image it comes with a boot loader, which is a piece of software that is started by the firmware. The boot loader’s primary function is to locate and load the operating system’s kernel, which is the core of the operating system responsible for managing hardware, memory, and processes. UEFI (Unified Extensible Firmware Interface) offers more advanced and flexible boot loading capabilities compared to legacy BIOS. One of the significant differences between UEFI and legacy BIOS is the transition from 16-bit to 64-bit architecture.

Legacy BIOS operates in a 16-bit processor mode, which has limitations in terms of memory addressing and processing power. It cannot load complex operating systems directly, so it utilized the MBR for booting. The MBR has limited space available which puts a restriction on the number of partitions and thus the number of operating systems that can be accommodated on a single drive. This constraint typically allows for only a few operating systems in a multi-boot setup using Legacy BIOS.

UEFI operates in a 64-bit mode and comes with the EFI Boot Manager, allowing it to access modern hardware capabilities and handle larger memory sizes efficiently. UEFI bootloaders can be stored in directories on the EFI System Partition, supporting different operating systems and configurations.The EFI Boot Manager provides a user-friendly interface that enables users to choose between different bootable devices and operating systems installed on the system. UEFI introduced the concept of Secure Boot, which ensures that only properly signed and authenticated bootloaders and operating system kernels are loaded, enhancing system security.


UEFI and Legacy BIOS share fundamental functionalities, with UEFI serving as the more modern and customizable alternative. UEFI offers advantages such as quicker boot times, expanded storage capabilities, heightened security features, and a modernized BIOS menu interface. It represents an advancement over legacy BIOS, conducting more comprehensive hardware checks, initialization routines, and simplifying driver updates. Despite UEFI’s superiority, legacy BIOS remains relevant, especially if your motherboard supports it. With a history spanning decades, legacy BIOS is suitable for lightweight operating systems or instances where a quick boot is needed.