UEFI vs Legacy BIOS: The Boot Mode Showdown – What You Need to Know

If you’re like most people, you probably don’t think about your computer’s BIOS and boot mode on a daily basis. But when it comes time to buy a new computer or upgrade an old one, the choice between UEFI vs Legacy BIOS boot becomes very important. So, how do you know which one to pick? In this article, we will take a look at what these two boot modes are, the benefits and limitations of each, and how they are different from one another.  

UEFI vs Legacy BIOS

How does a computer boot up?

The question sounds simple. You hit the power button, and the computer turns on, right? Well, it turns out to be a little more complicated than that. Here’s a quick rundown of what happens:

  1. The power button is pressed.
  2. The CPU starts the process by retrieving default boot instructions from a firmware chip on the motherboard. This is necessary as the CPU initially loads with no directions of its own. Once it has them, the CPU begins running them.
  3. The retrieved code performs a Power On Self Test (POST), verifying that the internal hardware is recognized and working properly. Afterward, it moves on to the external hardware, such as your mouse and keyboard, and verifies them as well. There is usually a visual and audible sign to signal the completion of this.
  4. The final task of the firmware code is to locate and initialize the boot loader. The boot loader is a small bit of code (limited to a space of 512 bytes) built to start up your Operating System (OS). Once this is detected, the boot loader is given control over the rest of the startup process. Some modern boot loaders are used to run a larger secondary boot loader in order to run a more complicated startup process.
  5. The main task of the boot loader is to locate and load the kernel: a central program of the OS with control over everything else in the system, being responsible for hardware and software interactions. Other essential programs such as wininit.exe, services.exe, lsass.exe, and lsm.exe are then loaded to handle the functions of service control, security, and local session management.
  6. Finally, after all of these processes have loaded alongside some extra drivers, you are presented with a Graphical User Interface (GUI), otherwise known as the login screen.

It’s important to reiterate here that this is a simplified overview of the startup process, as many other nuanced procedures occur during these steps.

What is the role of UEFI and Legacy BIOS during the boot process?

UEFI and Legacy BIOS are firmware interfaces that work as an in-between for the operating system and the computer firmware on the motherboard. When you start up your computer, these interfaces are used to initialize the hardware components and start up the operating system that is stored on your hard drive. 

What do UEFI and Legacy BIOS mean?

The abbreviation UEFI stands for Unified Extensible Firmware Interface, which works as a middleman to connect your computer’s firmware to the operating system. It is used in the initialization of all hardware components and the startup of your computer’s operating system. The information needed for initialization and startup is stored in a .efi file, which is stored on a special partition called the EFI System Partition (ESP). This partition also contains the boot loader programs needed for the operating system. 

UEFI Example - MSI Brand

Legacy BIOS, on the other hand, is an older boot method that was used on early personal computers during the MS-DOS era. BIOS stands for Basic Input/Output System, and it is a firmware that is embedded on the chip of your computer’s motherboard (pre-installed). It works by loading and waking up your computer’s hardware components, then loading up the boot-loader, which initializes your operating system. Because BIOS runs in a 16-bit processor mode and only has 1MB of space to execute these processes, it tends to lead to a slower boot process as it can only initialize one thing at a time. 

Legacy BIOS Example

How to check what boot mode you have

You can check whether you’re using UEFI or Legacy BIOS in the System Information window.

  1. Hit the Windows key on your keyboard and type in “System Information”, then open the application that appears. You can also accomplish this by holding the Windows key and tapping R, then typing in “msinfo32” and hitting the Enter key.
  1. In the window that opens, search in the list for BIOS Mode under the Item column. The Value column beside it will either read Legacy or UEFI, indicating what boot mode your computer uses.
System Information - BIOS Mode - Find Type of Firmware

What are the benefits of UEFI vs Legacy BIOS?

Before we look at the pros and cons of each of these systems, it’s important to note that UEFI was built to replace the Legacy (BIOS) system completely, so it certainly has a leg up on a few processes. That being said, Legacy (BIOS) still has its merits, and one system may be right for some while not being right for others. 

Here’s a technical rundown of the benefits of UEFI vs Legacy BIOS boot mode.


When saving information, Legacy (BIOS) uses the Master Boot Record (MBR) while UEFI uses the GUID (or Global Unique Identifier) Partition Table (GPT). 

The MBR uses a 32-bit entry system which allows you to place up to 4 partitions on a single drive, with the size of each partition being up to 2 terabytes (TB). This obviously runs into a problem, should you use any drive larger than 8 TB, as the extra space simply won’t be accessible. Additionally, the MBR is the only thing storing partition information, so if it somehow gets corrupted, it renders the entire disk unreadable. 

The GPT, on the other hand, uses a 64-bit entry system, dramatically increasing this size potential to a theoretical 9.44 zettabytes (ZB). For reference, 1 ZB is equal to 1 billion TB, so UEFI has the potential to operate almost unimaginably large systems. In addition to this, UEFI could theoretically handle an unlimited number of partitions in this space. However, most OSs will limit you to 256 TB of storage with a maximum of 128 partitions.

Choosing an incorrect partition style during OS installation can lead to the “Windows Cannot Be Installed to This Disk” error, which is caused by a mismatch between your GPT or MBR partition style and the selected UEFI or Legacy BIOS boot mode.


UEFI has the advantage of being independent of the platform it’s on, so it can potentially increase the overall speed of a computer and decrease its boot time. However, this depends entirely on how UEFI has been configured and is generally better suited to high storage systems. Additionally, the enhancement to boot time will go largely unnoticed as the difference will only be a fraction of what you’d normally experience. Typically, developers can make the most use out of UEFI by linking commands from other UEFI applications to optimize its performance.


UEFI wins out in this category with its Secure Boot feature, which was first implemented in Windows 8. Secure Boot works by forcing boot loaders to contain an authentic digital signature in order to access the kernel. This requirement puts a complete stop on things like malware, as they simply can’t obtain such a digital signature. That being said, this feature also makes it much more difficult to install a different OS on a Windows machine, such as Linux.

What are the limitations of UEFI vs Legacy BIOS boot mode?

When looking at the limitations of UEFI vs. Legacy, we see that UEFI only has a few disadvantages, but where it lacks may strongly sway your decision.

No backwards compatibility

UEFI has no compatibility with older OSs and can’t be used in any system older than Windows 8. Should you try to restore an old computer or require an older OS, UEFI will not allow you to boot from your boot disc to go through the reinstallation process. Legacy (BIOS) is compatible with both older and modern systems, so it’s more widely available and usable.

Cost of setup

Due to the coding complexity, UEFI requires a lot more labor in testing and development. In other words, motherboards running UEFI will be more expensive, as well as harder to troubleshoot should they experience a problem, despite their user-friendly GUI.


As we covered above, UEFI can handle much larger storage devices. However, it also requires larger storage devices in order to operate or even be installed. UEFI files are simply much larger than those of Legacy (BIOS) and need more space to operate effectively.

What is the main difference between UEFI vs Legacy BIOS?

UEFI and Legacy BIOS are both low-level firmware that operates on your motherboard to get the computer started and running smoothly. They differ in the method they use to accomplish this task. UEFI is the more modern boot mode intended to replace Legacy BIOS. 

Which boot mode should you choose: UEFI or Legacy BIOS?

As with most computer systems, the one you choose should be the one that aligns with what you want the computer to do. However, the three most important aspects of comparing UEFI to Legacy BIOS are functionality, adaptability, and overall speed.


The easiest way to compare this is by looking at what each system uses to run. Legacy (BIOS) uses Read Only Memory (ROM), a collection of files no larger than 64 KB. The issue ROMs most often face is that they need to be updated alongside hardware in order to function, so swapping out parts means upgrading the ROMs at the same time in order to avoid compatibility issues.

UEFI avoids this issue by using drivers. Drivers have a similar function to ROMs, but they don’t have the 64 KB storage limit and are built separately from the hardware that they’re meant to interact with. This difference means that drivers can be endlessly downloaded and installed separately as needed, all while being reconfigured by UEFI’s programming to ensure compatibility.


The programming language itself makes the biggest difference here. Legacy (BIOS) uses a programming language called Assembly, which due to its age, now runs codes that are often long and confusing. These are often made more confusing by coders attempting to bypass compatibility issues by writing their own work-around codes.

The programming language used by UEFI is called C-language, and it is much simpler and user-friendly. With how UEFI works, any code that may need to be written in can be done so much more easily and without the need to bypass features. This, in turn, makes the coding much more customizable.


As mentioned above, UEFI can be configured to optimize the boot process, making it start up faster than Legacy (BIOS). Again, the difference is fairly small and usually goes unnoticed, but when optimized properly in larger systems, it can be significantly faster.

FAQ: UEFI vs Legacy BIOS

Naturally, there’s far too much to cover on just this topic in order to flesh out every detail, but here are some additional questions you may still have.

Is UEFI the better choice?

In most cases, UEFI definitely has more to offer than Legacy (BIOS), but again, it still depends on what you want your computer to be able to do. Older computers require Legacy (BIOS), and smaller storage systems don’t need UEFI to run, but security and adaptability might be paramount for you. Factors like these are what you should base your decision on.

Is it possible to switch from Legacy (BIOS) to UEFI?

Yes. Often you’ll have to do this directly through your motherboard’s BIOS settings. You can look up how to access the BIOS on your motherboard manufacturer’s website.

How do I update UEFI (or BIOS)?

This is a process that can differ greatly depending on your motherboard. You can, and should, look up the exact process on your motherboard manufacturer’s website.


As with anything, it’s always best to make decisions based on what you need. In the case of UEFI vs Legacy (BIOS), both systems offer unique advantages and disadvantages, so be sure to compare those with the system you plan on running to find what’s best for you.

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