BIOS vs CMOS, Connections and Differences

by Kelvin
BIOS против CMOS

The first thing to understand is that BIOS and CMOS are obviously not the same thing, but they go hand in hand and you cannot understand one without the other. So, in order to know their differences, we must first understand their meaning and the function they serve.

BIOS vs CMOS, connections and differences


In this case, the BIOS is a logical part of the PC, that is, it is the program that is responsible for the correct start of the PC. Its abbreviation comes from Basic input-output system or basic I / O system and is nothing more than firmware, very compact and basic software that is installed in ROM memory.


This memory is a chip that is powered from an external power source to the PC’s power source itself, such as a battery, which, on the other hand, is the most common system in the industry.

It is required that this chip does not lose the configuration of the software included in it, such as hard drive startup options, RAM configuration, options selected at system startup, or anything that can be enabled or disabled in the BIOS itself. Another key point that is often overlooked is that thanks to this stack, the system time and date are preserved, so if we do not have automatic synchronization options for these two parameters in Windows, the ones belonging to the BIOS itself will appear.

Hence, this battery is the main part of the work we will be doing in the BIOS, where, depending on the model and the capacity they acquire, they tend to last up to 10 years on average without the need for replacement.

CMOS is the physical part of the equation

BIOS chip

This chip we talked about is nothing more than a CMOS system where it is shaped and built as a metal oxide semiconductor chip whose sole purpose is to house the BIOS, its configuration, updates, and the possible glitches that have them.

Thus, BIOS and CMOS are part of a single whole, motherboard and system. The first is the logical part, the second is the physical, and, obviously, they cannot live without each other. There are a few more curiosities, as CMOS got its name from the manufacturing technology of the chip itself, that is, it is incorrectly named.

CMOS is a technology for manufacturing integrated circuits where, for example, processors are located, so instead of saying CPU, we say CMOS. The correct name of the microcircuits in which the BIOS is located: EEPROM which is logically generated by CMOS.

Hence, EEPROM is a type of electrically erasable programmable read / write chip that allows data to be overwritten if the system allows it. On motherboards, this is very useful if there is damage to the BIOS and we need to overwrite it. Previously, this was not possible from the motherboard itself, and an EEPROM programmer was required to properly flash the chip.

CMOS vs EEPROM, why is there so much confusion?


Therefore, the so well-known “clean CMOS” should be called absolutely correct and accurate “clean EEPROM”, no doubt much more successful. By understanding the differences, we can already distinguish between what is right and what is not. Another example is exactly CMOS settings, when in fact we mean UEFI settings.

It also cannot be pronounced as a BIOS setting, mainly because motherboards have not had a BIOS for 10 years, but there is UEFI as such. Curiously, although EEPROMs with CMOS are increasing in size, the reality is that UEFI or BIOS, if such a situation arises, will only remain in the first MB, since it is verified that it weighs as little as possible, but add the maximum number of instructions.

Among other things, the EEPROM stores compatible hardware that needs to be recognized, usually it has the microcode of the processor manufacturer for that platform, in addition to recognizing, for example, solid state drives, video cards and other devices with which it can exchange or SKU or ID directly …

Usually in these cases, all these devices Plug and play so there is no need to configure anything for EEPROM and BIOS / UEFI, just check the CPU, RAM and GPU / GPU that they are compatible with the registered SKUs. in their microcodes. Otherwise, the motherboard will not turn on and we will have a beautiful black screen.

This often happens with multiple processor series for the same socket. The UEFI update is critical if we want the processor to recognize it. This is much more unusual in graphics cards, but there are also cases of problems due to the inability to read SKU or model IDs, and you even need to enable CSM to be able to go to Windows…

In short, we are talking about the whole, where some are the physical part and others the logical part, but it goes without saying that they are not even remotely the same, and yet many are still confused by the fact that there are people. who says BIOS instead of UEFI or even CMOS instead of EEPROM. So now we can name each of them correctly without getting confused.