How-To Geek

What Is UEFI, and How Is It Different from BIOS?


While most people may be familiar with a PC’s BIOS, they may not know what it is or what it does. Since UEFI is poised to take its place, let’s take a geek retrospective on these two  technologies.

Understanding BIOS (Basic Input/Output System)


(Image from richardmasoner)

The BIOS (pronounced “bye-ose”) is a computer’s Basic Input-Output System. It’s a low-level software that’s so important integrally that resides on a chip that’s built into the motherboard. When your computer starts up, it’s the BIOS’s job to wake up the various components and make sure they’re functioning, then it passes off functionality to your operating system or another boot loader. A “long” time ago, computers used very different and proprietary ways to do this, but over time IBM’s 5150 sort of became a standard on which to base hardware compatibility. It used the Intel 8088 processor which was 16-bit, and so the BIOS itself is 16-bit and is allowed 1MB of address space. It also uses a Master Boot Record, or MBR, to specify the computer’s partition table, which in turn tells the BIOS where the operating system is.

POSTing is a BIOS-governed process. It’s a power-on self-test which checks the validity and correct functionality of your components. If something is wrong, you’ll see an error displayed or hear a cryptic series of beep codes. You may also see the acronym CMOS. This refers to the battery-backed memory which is used in conjunction with the non-volatile RAM used with the BIOS. It’s actually not accurate anymore, since this method has been replaced with flash memory (also referred to as EEPROM) in contemporary systems.

phoenix bios

All in all it was a good system. It provided an interface from which you could enable/disable individual components and advanced hardware options. Of course, as with everything in the silicon world, BIOS obsolesced in comparison to the newer hardware that was developing. In order to make up for a lot of its shortcomings, extensions were developed. The prime example of this is Advanced Configuration and Power Interface, or ACPI, which was put in place to help device configuration and advanced power management functions. But, over time, it’s limitations needed to be overcome by a brand new system.

The Successor: UEFI

The Unified Extensible Firmware Interface, also known as UEFI (pronounced “oofy” or “U effy”) was originally developed by Intel to circumvent these issues for its 64-bit Itanium-based servers. Over time, it was renamed from the Intel Boot Initiative and given over to the Unified EFI Forum, which governs the specifications for it. UEFI brought some major changes to the pre-boot environment.


Many implementations of EFI just look like the traditional BIOS, but others customize the visual layout fundamentally. While pretty pictures aren’t really necessary, they can be really helpful for things like overclocking. Take a look at the differences:


As you can see, it’s easy to use, mouse-capable, and has a lot of potential.

msi click bios

MSI calls its version the “EFI Click BIOS.”

16-bit vs 32- and 64-bit

While the BIOS is limited to 16-bit processes and 1MB of memory addressing, UEFI isn’t constrained in that way. It can function in 32-bit and 64-bit modes, allowing much more RAM to be addressed by more complex processes. It also can be architecture independent and provide drivers for components that are also independent of what kind of CPU you have.


The MBR is limited to 4 primary partitions per disk and bootable disks are limited in size to 2.2 TB. UEFI uses the GUID Partition Table, which utilizes Globally Unique IDs to address partitions and allows booting from hard disks as large as 9.4 ZB. A terabyte (technically, a tebibyte) is 1024 GB, and a zettabyte (zebibyte) is 1024x1024x1024 GB. Seems pretty future-proof for the moment, no? And the benefits don’t stop there; UEFI allows more boot options, doesn’t prescribe particular file systems, and has excellent network booting abilities. OS boot loaders can also serve as extensions to the UEFI, which itself can function as a proper boot loader.


UEFI supports older extensions, like ACPI, which aren’t  dependent on a 16-bit runtime environment. Cryptic beep-code errors are also a thing of the past, as extensions can better test components (unless something more dire is wrong, like a bad processor). In addition, it support EFI-based partitions on hard disks which manufacturers can use to add more functionality. Asus’s Splashtop instant-on OS is a good example. While it works with BIOS, UEFI can offer better boot times and loading for something like that.



Its potential is what makes UEFI so promising. Not everything is optimal yet, but it operates already at BIOS level, so manufacturers have been starting to use it more on their motherboards. They can use older extensions with the new system until newer ones can take over, and the older visual style can also be used in the interim. The switch has been rolling out at an ever-increasing pace over the past few years. It’s not possible to put UEFI on BIOS-based motherboards, but odds are that when you buy a new system or perform an upgrade in the next few years you’ll be making the switch, perhaps without even realizing it. It’s a slow switch, but it seems to be an inevitable one.

Yatri Trivedi is a monk-like geek. When he's not overdosing on meditation and geek news of all kinds, he's hacking and tweaking something, often while mumbling in 4 or 5 other languages.

  • Published 03/25/11

Comments (37)

  1. Edi

    can you tell me the example motherboard use UEFI?

  2. kevin_Spencer
  3. rino

    about time! now if only applications will go all the way 64bit then we can say buh-bye to 32bit limitations.

  4. Neel

    can we access UEFI by pressing DEL? i guess no :P
    The UEFI is an installed software (Drivers & “Utilities”) from an installation CD/DVD that we get when purchased the motherboard IMO

    I have recently bought a motherboard about 1 month ago : MSI P55A-G55, after the installation of Chipset Drivers i saw “Utilties” which i guess IMO is the UEFI where in the manual i saw screenshots (Control Center) for accessing BIOS Profile, Overclocking, DRAM Configuration, Controling LED on motherboard, check MOSFET Temp..

    It offers a more friendly GUI compared to the traditional BIOS but can we installed it under linux environment? :S

    I’ll stick to my traditional BIOS interface xD

  5. Danny

    As a geek, it is in my nature to be pedantic.
    A ZB is a GB times 1024 four fold, not three.

    Still, great article. Well explained.

    @Edi. From the spec, this motherboard (for example) seems to have UEFI.

    @rino. Down with 32 bit :D My company bought me a laptop with 4GB of RAM but W7 32bit :C

  6. Carlos Ferrari

    So it will be like universal – both PCs and Macs – or is there some huge difference between UEFI and EFI?
    Hope it will be universal so finally OCing will be available to Macs. 8)

  7. A

    can this UEFI be downloaded and replace the existing bios on an older motherboard?

  8. Billyt

    Apple computers with an Intel processor and win2K3 server already use the Guid partition scheme

  9. B

    @ A – read the last paragraph.

  10. clive

    Its an P8P68 Deluxe clue is on the picture …….

  11. Jean

    Thanks. Useful (love the acronym pronunciation keys).

  12. Rich

    What do you mean by “…(perform) an upgrade?”

    It’s not possible to put UEFI on BIOS-based motherboards, but odds are that when you buy a new system or perform an upgrade in the next few years you’ll be making the switch, perhaps without even realizing it.

  13. Reznor

    @ Rich- You know, when you “preform an upgrade” meaning you “buy” a new motherboard to upgrade your system.

  14. Reznor

    Great article. Just wish people would RTFM or article entirely before you post your question. ( @ A )
    it’s a waste of keyboard types.

  15. KIM

    I keep getting blue screen error that refer to my BIO’s.
    Any suggestions, I have already reinstalled VISTA and upgraded to Windows 7?

  16. Reznor

    What does the Blue Screen Error state?

  17. Reznor

    Sorry, @ Kim, what does the error message say?

  18. KIM

    Check your BIO’S disable shadowing and something else. I will have to write them down again. If you installed any recent software. This desktop is only 4 years old and I have had it to two different repair places no one seems to know what the issue is….

  19. Jean

    II need a new computer soon; is it worth waiting for UEFI? It sounds like a real improvement. I tend to keep my machines as long as possible – my IBM ThinkpadiT41 is over 6 years old — and I’d dislike missing out on a significant new feature. I can hobble along with my T41 if there were a reasonable timeframe for UEFI….(How can one tell if it is installed? Is any particular manufacturer on the fast track to incorporate UEFI?.) THANKS. Jean

  20. Reznor

    Not in BIOS. Functions of your OS or IE.

    see Task Manager>Performance

    Maybe you need more ram or your ram is defective

  21. refurbman

    And technology marches on!

  22. raphoenix

    Where does the UEFI Machine Code reside ??

    On a Controller Chip, Built in to a Chipset, Built in to every CPU, etc…??

    It cannot reside on any particular hardware boot device as that would defeat its purpose.

  23. ed

    This is one of the clearest and readily understood things I’ve read in recent years. KUDO’s.

  24. Anonymous

    This probably isn’t a big deal but I do want to clear one thing up. (Isn’t this the catch phrase of every “geek”?)

    In the article it said, “It used the Intel 8088 processor which was 16-bit…” And I have to say that statement is somewhat misleading. The reason it is misleading is because the 8088 only had an 8-bit “external” bus. That meant the 8088 could only work as an 8-bit processor because it could only produce 8-bits of data each clock cycle. So, yes it was a 16-bit CPU internally and technically speaking, but because it was somewhat crippled by it’s 8-bit bus it could only work as a 8-bit CPU. (It’s this 8-bit bus which is why the successor line of 80188 line of CPU’s were shortly abandoned too).

    Therefore, I would have preferred the mention of the 8086 rather than the 8088. And that’s really my point here.

    For true 16-bit you should have mentioned the 8086. Because it was the 8086 – not the 8088 – which is the real the grand daddy of modern day PC’s. In fact, it was the 8086 which is what was “over developed” and eventually morphed into the 80486 – often referred to as simply a “486.” The concept really exploded when Intel started developing their Pentium line of CPU’s too. But you can still see the influence of the 8086 even then.

  25. IAmWEC

    I know that there were BIOS viruses many years ago that really didn’t amount to anything, but this seems like there is more to it, but there’s also more to go wrong. Say someone can crack into this. They can change some settings and make it unable to report the information it needs to to the OS. Say something breaks in the code, then the system is unable to boot. Just more to go wrong, as I see it.

  26. D. Frank Robinson

    I think an encrypted ‘BIOS’ to boot into UEFI would be a good security feature. Eh?

  27. Ikem

    UEFI. Good for remote control your PC without your knowledge.


  28. Richard's XP

    Very cool I have always been a fan of asus. I would like to try one of new asus boards with UEFI. What I am wondering is. Will these boards be compatible with any RAM and CPU that are are on the market now. Or will they need to be UEFI compatible. Or did I miss that in the wright up..

    @ Kim check your RAM volt settings, you may need to change them up or down. Depending on the board and RAM you have.

  29. Anonymous

    I’m not sure we have our facts right. The first time I ever saw a BIOS that a person could “adjust” was in a 80286 – not in systems based on 8088/8086 CPU’s. Back then, most computers based on the 8088 and 8086 were considered to be “XT” type machines, were often referred to as “clones” if they didn’t come from IBM, and did not have a BIOS that a user could adjust. It wasn’t until the “AT” which started with 80286 CPU-based systems that there was any kind of user interface to the BIOS settings.

    I just wanted to clear that up.

    Even more interesting is the reason some of those earlier systems were called “clones” too. That’s because a clone was able to load and run Microsoft’s Disk Based Operating System (MS-DOS) which was really just a slightly different version of IBM’s own PC-DOS (this was way before OS/2 or OS/2 Warp). And guess who the “developer” of IBM’s first PC OS was? Hint: it’s the same guy! And it was IBM’s BIOS that he had access to which allowed him get “his” OS work on those machines too.

    Yep! Not only did Bill Gates (legally) rip off Digital Research to obtain “his” operating system (a charge that’s rather common knowledge) but Bill Gates also (legally) ripped off IBM for their BIOS code too. I should say “probably” since it’s not something anyone can really prove. Not now that the worlds richest man has an army of lawyers who can bury any incriminating evidence – if it exists. About all that has been proven is that when IBM’s contract ended with Bill Gates that ‘ol Mister Bill almost immediately went into competition with IBM by selling his own version of the nearly the same identical operating system. And having an operating system that was already tweaked to work with a BIOS on what all the idiot business people were buying just made it that much easier.

    Nice guy, isn’t he? Sort of makes a you want to embrace Apple at least until you realize that Apple was founded by a stark raving dictatorial lunatic who’s probably worse!

  30. herval

    nice info anonymous…

  31. icusawme

    IBM pretty much let Mr. Bill have the OS business cause the DOJ was on them for the same reasons they went after Microsoft a few years ago. Gates was in the right place at the right time with what it took to get the job done (whatever “it” is)

  32. Thomas Clover

    Awesome article. Keep up the good work.

  33. bdxvmbxn

    There was a good thread on Slashdot about this 6 years ago:

    and even then it was obvious that this was a way to push DRM on to the consumer.

    We should reject this technology and demand BIOS, or (better) OpenBIOS.

  34. Neil

    “also known as UEFI (pronounced “oofy” or “U effy”)”

    Here is Europe we have a football (sorry… soccer…) governing body called UEFA – pronounced by the English speakers as “you-wafer”.

    UEFI is gonna become ‘you-wafee”, I’m already struggling to read it any other way.

  35. fstd

    But will it run Lunix??

  36. jimbo

    Sorry I am not clear to the answer to this simple questions. Is UEFI bios replacing traditional BIOS or is it in addition to traditional BIOS? Basically, if I buy a board ASROCK H67M-ITX/HT which states UEFI is required to have 64 bit vista or 7, if i buy that board my only options for os is 64 bit vista or 7. what if i want to install xp 32 bit? is it going to look like the traditional bios or will i not be able to install xp 32 bit. please no tripe comments just a straight answer.

  37. rishabh

    how do i know if i have UEFI ?

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