How a computer works?

Computers, aren't they interesting? Before we dig deep into explaining how a computer works, you must know what is a computer. A computer is any device that is used to store or transfer any information either with or without the internet. There are different types of computers, however, for this topic, we are going to focus on desktop/ laptop PCs.

A desktop/ laptop computer is made up of multiple components that are put together to form one PC, components like a power supply, motherboard, CPU, graphics card, hard drive, ventilation fans, cables, etc., and many more which we will get into in detail in a later blog but for now, just understand one thing and that is all these computer components make up one functioning PC. First, let's find out what actually happens when you push that power button in your PC.

What happens when a user tries to power on a computer (desktop and laptop)?

The following process happens:-

1. At first, the BIOS (basic input output service) firmware built into the motherboard stored on the BIOS chip starts up. It is responsible for initializing the computer’s hardware as it is being booted. It contains sets of instruction that need to be performed with the help of CPU to make sure all components of the computer including the OS (Operating System) is healthy before presenting it to the user. The BIOS chip is non-volatile which means the contents in the chip are retained even after the power is turned off.

2. It does POST (power on self-test). It makes sure all the components are working correctly and that the hard drive is installed correctly and in usable condition since OS is located in the hard drive of the computers.

3. If the test is passed usually in older models of computers it makes a single short beep.

4. BIOS will then search for a hard drive to boot the OS.

5. Finally, the BIOS connects to the bootloader program, which wakes up the computer’s operating system and loads it into the RAM.

6. Whatever configuration the user has done on BIOS like date & time setting, boot sequence, hardware settings, fan speed, etc.. will all get stored in a chip called CMOS (Complementary metal oxide semiconductors). The CMOS chip, unlike the BIOS chip, is volatile and therefore to retain its contents there is usually a battery located on the motherboard to power the chip.

7. In other words, BIOS is the firmware/program that comes inbuilt with the motherboard which is stored in the BIOS chip, whereas CMOS is a chipset where the changes made to BIOS get stored into.

Additional points:

The BIOS now has an updated version called UEFI (Unified Extensible Firmware Interface) which is in built-in modern motherboards instead of BIOS in a read-only memory (ROM) chip and has replaced BIOS in modern computers. UEFI also supports a GUI interface far better than old BIOS. The main difference between the BIOS and UEFI is in how these two firmware execute their functions. However, the main function of BIOS/ UEFI is to conduct a POST assessment and find the bootloader to make sure every component in the computer is working properly and is ready to serve the user.

Basically, BIOS/ UEFI instructs the entire computer system on what frequency the CPU, GPU, and RAM should operate, as well as how much power they should draw from the PSU (Power Supply Unit). The fan speeds, RAM latency, and other hardware-related settings are also decided by this low-level software. However, if certain settings are changed in the BIOS or UEFI like time, fan power, etc. then the BIOS/ UEFI will check the CMOS/ NVRAM chip for the user's custom settings and operate and instruct the computer accordingly.

But nowadays in modern motherboards, CMOS is replaced by NVRAM (non-volatile RAM) to store changes made to the BIOS or UEFI since it can retain power even when the computer is disconnected from power even without a battery unlike the CMOS chip where by default it is volatile and to make it non-volatile the battery was used. Although CMOS was replaced by NVRAM for the convenience of speed, the number of bits it can store, and power retention, a battery is still present in most computers as the battery's main functionality is to manage the clock settings of the computer which helps in real-time clock management ensuring the clock settings are synced.