This article serves as a professional guide on What is BIOS in Computer. It provides in-depth insights, step-by-step explanations, technical clarity, and a beginner-friendly understanding of how BIOS works inside a computer system. Read on for a comprehensive overview and valuable tips.
If you have ever wondered what happens inside your computer the moment you press the power button, the answer begins with BIOS. Before Windows, before the login screen, and before any software loads, BIOS quietly performs its job.
Many beginners hear the word BIOS but do not fully understand its importance. Some think it is software. Some think it is hardware. Some believe it is inside the CPU. In this article, we will clear all confusion.
We are exploring What is BIOS in Computer, how it works, its functions, types, settings, comparison with UEFI, troubleshooting, real-life examples, and expert tips.
Let’s explore it together!
Table of Contents
What is BIOS in a computer?
BIOS is a small program stored on a special chip on the motherboard of a computer. It runs immediately when you press the power button.
BIOS checks whether all hardware components are working properly and then loads the operating system.
In simple words:
BIOS is the startup manager of your computer.
Without a BIOS, your computer cannot start.
BIOS Full Form in Computer
BIOS = Basic Input/Output System
Let us understand each word:
- Basic – It performs fundamental operations.
- Input – It manages devices like the keyboard, mouse, and USB.
- Output – It controls the monitor display and output devices.
- System – It manages the startup system process.
It is called “basic” because it performs the most essential startup tasks.
Why is BIOS important?
BIOS is extremely important because:
- It starts your computer.
- It checks the hardware condition.
- It loads the operating system.
- It manages boot order.
- It stores important system settings.
If the BIOS fails, your system will not boot at all.
Even if Windows is perfectly installed, without a BIOS, nothing will work.
Where is BIOS Stored?
BIOS is stored on a small chip attached to the motherboard.
Earlier, BIOS was stored in:
- ROM (Read Only Memory)
Modern systems use:
- EEPROM (Flash Memory)
This allows BIOS updates.
Important points:
- BIOS is NOT stored in RAM.
- BIOS is NOT inside the CPU.
- BIOS is on the motherboard.
How BIOS Works (Step-by-Step Process)
Let’s understand what happens when you press the power button.
1. Power On – Electricity Activates the System
When you press the power button:
- The Power Supply Unit (PSU) starts supplying electricity.
- Voltage flows to the motherboard.
- CPU, RAM, storage drives, and other components receive power.
At this stage, the operating system is still not running.
The CPU does not yet know what to do. It needs instructions.
So the CPU immediately looks for the first program stored in a predefined memory location on the motherboard — and that program is BIOS.
Think of this stage as:
“Waking up the hardware.”
2. BIOS Activates – The First Program Runs
As soon as power is supplied:
- The CPU resets itself.
- It searches for firmware instructions.
- It finds BIOS stored on a flash memory chip on the motherboard.
- It begins executing BIOS code.
BIOS runs before:
- Windows
- Linux
- Any application
- Any driver
BIOS is the very first software (firmware) that runs on your computer.
At this stage, BIOS takes control of the system.
3. POST (Power-On Self Test)
Now BIOS performs a very important test called POST.
POST means:
Power-On Self Test.
This is a diagnostic test to check whether essential hardware components are working properly.
BIOS checks:
- RAM (Is memory detected?)
- CPU (Is the processor responding?)
- Hard drive / SSD (Is storage available?)
- Keyboard (Is the input device connected?)
- Mouse
- Display (Can video output work?)
If everything is fine:
System continues normally.
If something is wrong:
- BIOS may show error message.
- BIOS may give beep codes (long or short beeps).
- Computer may stop booting.
Example:
- Continuous beep → RAM problem.
- No display → Graphics issue.
- No boot device → Hard disk problem.
POST ensures that hardware is safe and ready before loading operating system.
4. Hardware Initialization
After POST is successful, BIOS prepares the hardware for operating system use.
This process includes:
- Allocating memory (RAM setup)
- Detecting connected USB devices
- Initializing graphics card
- Configuring CPU settings
- Enabling storage controllers
- Setting system clock
BIOS reads configuration settings stored in CMOS memory.
These settings include:
- Boot priority
- System date and time
- Enabled/disabled ports
- CPU configuration
- Security settings
At this stage:
Hardware becomes fully ready for OS loading.
5. Boot Device Selection
Now BIOS must decide from where to load the operating system.
It checks the boot order list.
Common boot devices:
- SSD
- HDD
- USB drive
- CD/DVD drive
- Network boot (in some systems)
BIOS checks devices in order.
For example, If boot order is:
- USB
- SSD
- HDD
Then BIOS will:
- First, check the USB for the OS.
- If no OS found, check the SSD.
- If SSD has Windows, it loads from there.
If no bootable device is found:
Error message appears: “No Bootable Device Found”
This step ensures the system loads the OS from the correct storage.
6. Load Operating System
Once BIOS finds a bootable device:
- It locates the boot sector.
- It loads a small program called Bootloader.
Bootloader examples:
- Windows Boot Manager
- GRUB (Linux)
- Other OS boot managers
Now the bootloader takes control.
Bootloader then:
- Loads the operating system kernel.
- Starts system services.
- Displays Windows or Linux startup screen.
At this moment:
BIOS hands over control to the operating system.
BIOS job is complete.
The operating system now runs independently.
5 Main Functions of BIOS
Here are the five major functions:
- POST Testing: Checks hardware health during startup.
- Hardware Initialization: Prepares CPU, RAM, storage, and devices.
- Boot Management: Selects device to load operating system.
- System Configuration: Stores date, time, boot order, and hardware settings.
- Security Control: Allows BIOS password protection.
BIOS Settings Explained
When you enter the BIOS, you can see different settings.
Common BIOS options:
- Boot priority
- System time & date
- Enable/disable USB ports
- CPU virtualization
- Fan control
- Secure boot
- BIOS password
These settings are stored in CMOS memory.
What is CMOS?
CMOS stands for Complementary Metal-Oxide Semiconductor.
It stores:
- BIOS settings
- Date & time
- Hardware configuration
It uses a small CMOS battery.
If the CMOS battery dies:
- Date resets
- BIOS settings reset
Types of BIOS in a Computer
There are mainly two types:
1. Legacy BIOS
- Old traditional version
- Text-based interface
- Limited features
- Uses MBR partition
2. UEFI (Modern Replacement)
- Graphical interface
- Mouse support
- Faster boot
- Secure boot feature
- Supports GPT partitions
- Supports large storage
Most modern computers use UEFI.
BIOS vs UEFI (Qucik Comparison)
| Feature | BIOS | UEFI |
|---|---|---|
| Interface | Text | Graphical |
| Boot Speed | Slower | Faster |
| Storage Support | Up to 2TB | Very large drives |
| Security | Basic | Secure Boot |
| Partition Type | MBR | GPT |
| Mouse Support | No | Yes |
UEFI is modern and more secure.
BIOS in Windows 10 and Windows 11
Even in Windows 10/11 systems:
- BIOS runs before Windows starts.
- It loads Windows boot manager.
- It controls startup configuration.
Modern Windows systems use UEFI instead of traditional BIOS.
BIOS in Laptop
BIOS in laptop works same as desktop.
It:
- Starts laptop
- Manages battery settings
- Controls power management
- Detects hardware
- Loads operating system
Each brand has slightly different BIOS interface.
Is BIOS Software or Hardware?
BIOS is firmware.
It is:
- Not normal software
- Not a hardware component
It is low-level system firmware stored on the motherboard chip.
So the correct answer:
BIOS is firmware.
Is BIOS in RAM or ROM?
BIOS is stored in ROM or flash memory.
- RAM is temporary.
- BIOS is permanent.
- RAM clears after shutdown.
- BIOS remains stored.
Is BIOS in the CPU or the motherboard?
BIOS is located on the motherboard.
CPU executes BIOS instructions.
But BIOS physically exists on the motherboard chip.
How to Open the BIOS in Computer?
Restart PC and press the special key:
- F2
- Delete
- F10
- ESC
Press immediately after powering on.
From Windows:
Settings → Recovery → Advanced Startup → UEFI Firmware Settings
How to Check BIOS Version?
Checking your BIOS version is important if you are planning to update it, troubleshoot issues, or confirm hardware compatibility.
There are two easy ways to check your BIOS version.
1. Using Windows (Recommended)
This is the easiest and safest method.
Steps:
- Press Windows + R on your keyboard.
- Type msinfo32 and press Enter.
- The System Information window will open.
- Look for “BIOS Version/Date” on the right side.
You will see:
- BIOS manufacturer
- BIOS version number
- Release date
This method works in Windows 10 and Windows 11 and does not require restarting your computer.
2. From BIOS Setup Screen
You can also check the BIOS version directly from the BIOS menu.
Steps:
- Restart your computer.
- During startup, press:
- F2
- Delete (DEL)
- F10
- ESC
(Key depends on your motherboard brand.)
- Once the BIOS screen opens, look under:
- Main tab
- System Information
- Top of the screen
There you will find the BIOS version and date.
Advantages & Disadvantages of BIOS
Before understanding whether BIOS is suitable for modern systems, let’s examine its key advantages and disadvantages in a clear and practical way.
Advantages
- Provides simple system control for basic configuration.
- Allows users to set boot order, date, and hardware settings.
- Known for stable and reliable startup performance.
- Offers low-level hardware access before the operating system loads.
- Works independently of the operating system.
- Useful for basic troubleshooting and recovery.
Disadvantages
- Supports only up to 2TB storage (MBR limitation).
- Has a text-based interface with no mouse support.
- Slower boot speed compared to modern UEFI.
- Lacks advanced security features like Secure Boot.
- Limited support for modern hardware technologies.
Real-World Example
Imagine your laptop turns on, but Windows does not start.
Possible reasons:
- Boot order wrong
- Hard drive disabled
- USB drive set as first boot device
You enter the BIOS and fix the boot priority.
The system starts normally.
That shows BIOS control over startup.
BIOS in Computer Class 9 (Simple Definition)
BIOS is a startup program that helps a computer check hardware and load the operating system.
This is a simple explanation suitable for students.
How to Update BIOS Safely?
- Visit the official motherboard website
- Download the correct BIOS file
- Check the motherboard model
- Backup important data
- Install the update carefully
Warning: If update fails, motherboard may stop working (called bricking).
Never install BIOS from an unknown source.
FAQs:)
A. No, BIOS is stored in ROM or flash memory.
A. No, BIOS is on motherboard.
A. Restart PC and press F2, DEL, or F10.
A. To start computer, check hardware, and load operating system.
A. POST (Power-On Self Test) is a diagnostic test performed by BIOS to check whether hardware components are working properly.
A. BIOS is stored on a small flash memory chip attached to the motherboard.
A. Traditional BIOS is mostly replaced by UEFI in modern computers, but many people still refer to UEFI as BIOS.
A. BIOS stands for Basic Input/Output System.
A. BIOS is a small program stored on the motherboard that starts your computer and loads the operating system after checking hardware components.
A. If BIOS fails or becomes corrupted, the computer will not boot. The screen may stay blank or show error messages.
A. The main purpose of BIOS is to initialize hardware, perform system checks (POST), and load the operating system.
BIOS is firmware. It is not regular software and not pure hardware — it is a program stored on a motherboard chip.
A. No. Without BIOS (or UEFI), a computer cannot start or load the operating system.
Conclusion:)
BIOS is the foundation of every computer system. It controls the startup process, checks hardware components, and loads the operating system safely. Even though it runs silently in the background, it plays a critical role in system stability and performance.
If you truly want to understand how computers work internally, learning BIOS is the first and most important step.
“Understanding BIOS is the first step toward mastering how computers truly work.” – Mr Rahman, CEO Oflox®
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Have you ever explored BIOS settings on your computer? Share your experience or ask your questions in the comments below — we’d love to hear from you!