BIOS, CMOS, UEFI – What’s the difference?
what is the BIOS CMOS and UEFI so that’s
what we’re going to talk about in this
video
now BIOS stands for basic input/output
system the BIOS is firmware that’s built
into the motherboard that initializes
the computer’s hardware as the computer
is being booted and then after it
initializes the hardware it then
searches for a boot device such as an
optical drive or a storage drive to boot
software such as an operating system
so from the start when you first turn on
the computer the computer does what’s
called a power-on self-test or post
which is run by the bios it tests the
computer to make sure all the
requirements are met and if the hardware
is working correctly before starting the
operating system if the computer passes
the test
the internal speaker will make a short
single beep which indicates that the
computer has passed the test and is
booting up normally however if there are
no beeps or multiple beeps then that
means that the computer has failed the
test and something is wrong and the
computer needs further troubleshooting
to find out what the problem is so
whether there are no beeps or multiple
beeps the computer will generate a beep
code to help you pinpoint the problem so
for example if the computer generates
three long beeps then that could
indicate a keyboard error or if the
computer generates a continuous short
beep then that could indicate a problem
with a RAM module so whatever BIOS is
installed on the computer’s motherboard
you can always refer to the
manufacturers documentation to find a
list of beep codes and what they mean so
you can pinpoint the problem and correct
it the BIOS software is stored on the
BIOS chip on the motherboard the BIOS
chip is non-volatile which means that
the contents of a chip are retained even
after the power is turned off but even
after the computer is turned off the
computer does need to maintain certain
settings such as the date and time the
boot sequence and certain hardware
settings in other words the custom
settings that you have configured in the
BIOS and these settings are stored on
the motherboard in a special chip called
a CMOS chip but unlike the BIOS chip
which is non-volatile the CMOS chip is
volatile meaning that it needs constant
power to maintain its contents or
settings so in order for the CMOS to
maintain its settings while the computer
is turned off
it uses a battery and this battery is
called the CMOS battery the CMOS battery
is a small button cell battery which can
be seen on the surface of the
motherboard and it’s usually located on
the bottom right hand corner and it’s
basically the same type of battery that
is typically used in wristwatches now as
I stated before the CMOS needs constant
power that is supplied by the battery
but if the battery is removed and then
reattached the BIOS will reset back to
its default settings from the
manufacturer and erase any custom
settings that you have configured now a
lot of people get confused about what’s
the difference between the BIOS and CMOS
and these terms are often used to refer
to the same thing but they are different
so just to clarify things the BIOS is
the actual firmware or program that
comes with your motherboard and that
firmware is stored in the BIOS chip but
the settings that you actually make to
the BIOS such as a date and time the
boot sequence fan speeds and things like
that those settings are retained in the
CMOS chip now the CMOS chip is not
necessarily its own chip on modern
motherboards it’s been integrated with
the real-time clock that’s part of the
Southbridge chipset
now a new type of BIOS is called UEFI
UEFI stands for unified extensible
firmware interface now most if not all
new motherboards are shipped with this
newer type of BIOS UEFI has several
advantages over the old BIOS and the
first and most obvious just by looking
at it is that it has a user-friendly
graphical user interface that supports
different colors and even animations
whereas the old BIOS has your typical
blue screen that resembles the windows
blue screen of death UEFI can also
recognize larger storage drives and you
can even use a mouse in the UEFI
interface where as compared to the old
BIOS where mouse support wasn’t even
available and you had to use your
keyboard only and UEFI also has a
built-in feature called secure boot and
secure boot stops any digitally unsigned
drivers from loading and it also helps
to stop malicious software such as
rootkits
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