What is BIOS (Basic Input/Output System) and why is it so important??

Long before your desktop lights up with icons and wallpaper, your computer runs through a hidden sequence of checks and setups. This behind-the-scenes routine is powered by the Basic Input/Output System (BIOS), the low-level firmware that readies your system hardware and boots the operating system. It acts as the link between your hardware and software, ensuring smooth communication between the two.

BIOS also plays a critical role in the security and performance of your system. To understand it all, let us delve into this article, which breaks down what is BIOS, how it works, and why it is so important for your system.

What is BIOS in computer systems?

BIOS, or the Basic Input/Output System, is a firmware stored on a small memory chip on the motherboard. As soon as you turn on your computer, the BIOS gets to work. It begins by initializing and testing your system’s hardware components and then loading the bootloader, which, in turn, loads the operating system. Its core function is to manage the data flow between your computer’s operating system and the peripheral devices like the keyboard, mouse, hard drives, and display.

The original concept of BIOS can be traced back to 1975, when computer scientist Gary Kildall used it to enable his operating system, CP/M, to operate on different systems without requiring major adjustments.

Later on, in 1981, inspired by this concept, IBM created its own version of the BIOS from scratch for the IBM PC. This BIOS was specifically designed to work with their hardware components. This proprietary BIOS was quite important because it was the only way to get a new IBM PC to work.

After IBM's BIOS became a key component of the PC, other companies began creating PC clones. This led to a new market where companies like AMI and Phoenix Technologies reverse-engineered the BIOS to create and license their own legal, compatible versions. 

This competition resulted in an explosive growth of the PC market, and for years, these third-party BIOS implementations became the industry standard. However, their limitations eventually led to the development of modern UEFI firmware, which offers enhanced security, faster boot times, and greater flexibility.

What is the purpose of BIOS?

The basic purpose of BIOS is to initialize and test system hardware to ensure that essential components are working; and then identify a boot device, load its boot sector, and hand over control to the bootloader, which can load the operating system from mass memory. 

Beyond this, BIOS also offers an abstraction layer for the hardware, without which the operating system would need to be programmed to know the exact technical specifications of every single brand of keyboard, mouse, hard drive, and graphics card.

Simply put, the BIOS acts as a simplified interface. It takes a complex instruction from the operating system and translates it into the precise, low-level commands that the specific brand of hardware understands.

How does BIOS work?

Here is a quick rundown of how BIOS works in a sequential order:

1. Power-up and initialization: When the computer is powered on, the CPU looks for the BIOS firmware stored in the motherboard's non-volatile memory.

2. Power-On Self-Test (POST): BIOS runs POST, a series of diagnostic tests that check essential hardware components like CPU, memory, disk drives, and input/output devices to ensure they are all functioning properly. If any hardware issues are detected, BIOS may halt the boot process and signal errors via beep codes or display messages.

3. Hardware initialization: The next step is to initialize the hardware devices, such as the keyboard, video display, and storage controllers, making them ready for use.

4. Boot device selection: The BIOS then identifies the configured boot devices (hard drive, SSD, USB, optical drive, etc.) in a specified order and selects the first bootable device.

5. Loading the bootloader: After selecting the boot device, the firmware on the BIOS/MBR systems reads the first sector of the bootable device (the 512-byte Master Boot Record) into memory and executes it. This sector contains a small bootloader program that begins the loading process of the OS. On the other hand, on modern UEFI/GPT systems, the firmware looks for a bootloader program (such as GRUB or Windows Boot Manager) stored on a special EFI System Partition (ESP) and executes it.   

6. Operating system handoff: Here, the control is handed over to the operating system, which then completes system initialization by running its own kernel, loads the necessary drivers for all connected devices, and finally, shows you the login screen or the desktop.

7. BIOS setup access: Before the OS loads, BIOS may also allow the user to enter a setup menu to configure hardware settings such as boot order, system time, CPU clocks, and security options.

Additional read: A guide to high-quality network design for MSPs

What are the different types of BIOS?

Mainly, there are two primary types of system firmware: Legacy BIOS and UEFI. BIOS, as we know, is the original firmware, and UEFI is the modern replacement with advanced features. Here, we discuss how firmware has evolved, from the text-based Legacy BIOS to the UEFI and some of its equivalents.  

1. Legacy BIOS

Legacy BIOS refers to the original BIOS interface that was used in older PCs and stored on ROM. It performs hardware initialization sequentially and uses the Master Boot Record (MBR) for the boot process.

2. Extensible Framework Interface (EFI)

Originally developed by Intel in the late 1990s and early 2000s, EFI allowed modular firmware architecture, enhanced boot management, and better hardware abstraction. It also provided a more scalable and flexible pre-operating system environment.

3. Unified Extensible Firmware Interface (UEFI)

UEFI is the modern evolution of EFI, standardized and maintained by the UEFI Forum. It has largely replaced legacy BIOS and EFI in modern PCs, bringing improvements such as Secure Boot, faster parallel initialization of hardware, and comprehensive support for large drives via GPT.

4. Mac equivalent

For Apple Mac systems, the equivalent BIOS firmware interface was Open Firmware, based on the Open Firmware standard created by Sun Microsystems and other industry partners. It provided hardware initialization and boot management, similar to BIOS, on Mac PCs. But when Apple transitioned to Intel processors in 2006, it replaced Open Firmware with EFI. On Apple Silicon Macs, iBoot, a secure bootloader, further replaces EFI. 

What are the key functions of BIOS?

From testing and initializing hardware to loading the operating system, BIOS carries out its work through four key functions. Let us take a detailed look at each of these functions.

1. Power-On Self-Test (POST)

During POST, BIOS performs an initial verification of the essential hardware components. This process is a set of diagnostic tests, and here is a detailed look at what happens:

• CPU check: The BIOS first starts by testing your processor.

• BIOS ROM verification: After that, the BIOS code is fetched from the ROM or flash memory and executed. Some implementations even perform integrity checks to ensure that the firmware is not corrupted. 

• Memory test: RAM is scanned for errors.

• Device detection: Essential peripherals like your keyboard and hard drive are checked.

• Configuration cross-check: Finally, the BIOS compares system settings with the data stored in the CMOS memory, which typically contains your system’s hardware configuration settings. 

• Error codes: If there are any errors encountered during POST, the BIOS will immediately stop the boot process and notify you. You will probably see a display text or hear a series of beep codes. 

2. Bootstrap loader

After the POST is completed successfully, BIOS locates and loads the operating system's bootloader from the designated storage device into the computer’s memory, enabling the OS to start. Here is how this happens:

• Scanning for boot devices: The BIOS checks the storage devices (hard drives, SSDs, USB drives, etc.) in a pre-configured order to find a bootable device. This boot order is something you can change in the BIOS settings.

• Locating the boot sector: Once it finds a bootable device, the bootstrap loader looks for a specific, tiny piece of code on that drive called the boot sector. On an MBR (Master Boot Record) formatted drive, this is the first sector of the disk.

• Loading the bootloader: The bootstrap loader's job is to read this boot sector code and load it into the computer's memory.

• Handing over control: Finally, the bootstrap loader hands over control of the computer to the code it just loaded. This code is the bootloader (e.g., Windows Boot Manager or GRUB for Linux), which is a much more complex program. The bootloader then takes over the task of loading the full operating system into memory and starting it.

3. BIOS drivers

BIOS drivers are small, low-level programs stored in the BIOS ROM. Their main purpose is to enable the CPU to communicate with and control the basic hardware components of the computer, such as:

• Keyboard: To allow user input during the boot process.

• Video card: To display text and graphics on the screen.

• Hard drives: To read data from the storage devices.

These drivers are extremely basic and only provide enough functionality to allow the system to complete the boot process. Once the operating system's bootloader takes over, it loads its own, much more comprehensive set of drivers that enable the full functionality of all connected hardware.

4. BIOS (CMOS) setup

BIOS also includes a CMOS setup interface where users can configure hardware-level options such as system clock, boot order, and security settings. These configuration options are saved in a small Complementary Metal-Oxide-Semiconductor (CMOS) memory chip on the motherboard.

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Why is BIOS so important?

It is easy to see why BIOS is so important when you consider the fact that it acts as the initial brain of your computer. Without it, your system would not know how to start, what hardware is connected, or how to get the operating system up and running. These points clearly demonstrate why BIOS is so critical:

• Through POST, it verifies that the computer’s architecture can complete the initialization procedure.

• Helps the computer locate the OS and complete the boot process.

• Loads the bootloader from the MBR or EFI System Partition, which then loads the OS.

• Helps address performance issues and protects systems from security threats through regular updates.

• For IT professionals, BIOS provides granular control over hardware settings that can improve speed, reliability, and handle bigger bandwidth as systems grow.

BIOS manufacturers

Originally developed by IBM, the legacy BIOS firmware was later reverse-engineered by Phoenix Technologies, which enabled companies like Compaq to build IBM PC clones. This opened the market for non-IBM computers, and today, manufacturers such as AMI, Award, Dell, HP, Asus, Foxconn, Lenovo, and Ricoh continue to produce BIOS implementations. 

BIOS and security

The BIOS is not just about getting your system started; it is also your computer’s initial line of defense. It sets the rules for security long before the operating system even starts to load.

Key security features of a BIOS include:

• BIOS passwords: A BIOS password can be set to protect the firmware's settings and to prevent the system from booting entirely without a valid password. This provides a basic layer of protection against unauthorized access.

• Boot order control: By controlling the boot order, a BIOS can prevent an unauthorized user from booting from a removable device (like a USB drive) and gaining access to data or installing a different operating system.

• Trusted Platform Module (TPM) support: On some motherboards, the BIOS can be configured to work with a TPM, a dedicated hardware chip that stores cryptographic keys. This enables features like full-disk encryption (e.g., BitLocker in Windows) by securely tying the encryption keys to the specific hardware.

• Secure Boot: A feature of UEFI, the modern firmware, Secure Boot ensures that only signed and trusted bootloaders or operating systems can run. This prevents malware or unauthorized software from loading before the OS, strengthening the overall security of the system.

Additional read: Maximizing security and efficiency with the SuperOps and ESET integration

What is the difference between BIOS and UEFI?

UEFI is a modern firmware interface that is designed to replace legacy BIOS. While both perform the same basic function of preparing a computer to boot an operating system, UEFI offers many advancements over the decades-old BIOS architecture. Let us understand their differences with the help of this table. 

Additional read: Know your storage formats - key differences between NTFS and FAT

How to access BIOS?

You can access the BIOS setup using different methods. These methods are mentioned below:

1. Using the BIOS setup key during startup

• Turn on or restart your computer.

• Press the BIOS setup key repeatedly immediately after powering on until the BIOS menu appears.

• The exact key might depend on your computer or motherboard brand (e.g., F2 or Del for Asus, F10 for HP, F12 for Dell, F1 or F2 for Lenovo).

2. Access BIOS via Windows Settings

• Open Settings > System > Recovery. For Windows 10 users, go to Settings > Update & Security > Recovery.

• Under Advanced Startup, click Restart now. Your system will reboot to a special menu.

• When the computer restarts, select Troubleshoot, then Advanced options, then UEFI Firmware Settings.

• Click Restart to boot directly into BIOS.

3. Restart with the Shift key

• In Windows, hold the Shift key and click Restart from the Start menu or power options.

• The system reboots to the Advanced Startup Options menu.

• Select Troubleshoot > Advanced options > UEFI Firmware Settings.

• Click Restart to enter BIOS.

What are the uses of BIOS?

Once inside the BIOS Setup Utility, you can use the menu to view system information, modify hardware configurations, and enable/disable certain features. It can be used to:

• Change the boot order.

• Restore the manufacturer’s default settings in case of misconfiguration.

• Update the firmware by using built-in update tools or utilities provided by the manufacturer.

• Change the drive and memory setting.

• See the total memory installed, including speed and slot usage.

• Adjust cooling profiles for better temperature management.

• Monitor real-time system health.

• Observe voltage readings for CPU, RAM, and motherboard components.

Additional read: Benefits of having network monitoring together with your unified platform

Common BIOS error codes and their fixes

Common BIOS error codes are typically signaled through beeps or on-screen messages. In addition to that, you may encounter issues like a boot loop, update issues, or a BIOS crash and freeze. All these errors and their fixes are discussed below. 

1. Failed to overclock error

This error often appears when BIOS settings have been cleared or when an overclock attempt fails. Overclocking RAM or CPU pushes hardware beyond its design limits, increasing heat and potentially damaging components.

Fix: Restore BIOS settings to optimized defaults by loading a pre-saved BIOS profile or resetting BIOS to defaults.

2. Short beeps

Two short beeps usually indicate a parity error in the memory. It means there is a problem with the RAM’s parity check, which is a method to detect errors in memory data. Sometimes, you can hear three short beeps, which typically signal a memory error in the first 64KB block of RAM (base memory error).

Fix: Check and replace the RAM or the motherboard if faulty.

3. BIOS boot loop (Constant restarting)

This happens when the PC powers on, shows a logo or fan noise, but then restarts repeatedly without booting into Windows. This can happen when your system has corrupted BIOS settings or failed overclocking attempts, or incompatible new hardware like RAM or CPU.

Fix: Perform a CMOS reset by removing the motherboard battery for 5 minutes or using the CMOS jumper. If a BIOS update causes this issue, reflash the BIOS using a recovery tool or the USB flashback feature. 

4. BIOS not detecting boot drive

When the BIOS does not find the bootable drive, you can face “No bootable device” errors. This can be due to loose cables, inaccurate boot priority, physical drive failure, or SATA port disabling (e.g., when using M.2 SSDs).

Fix: Enter BIOS settings and verify the drive is detected under Storage/Boot options. You can try checking the physical connections and changing SATA ports if applicable..

5. BIOS freezing or crashing

If the BIOS menu is unresponsive or the system freezes during the POST, this can be due to a corrupted BIOS firmware, faulty RAM, a failing motherboard, or defective peripherals.

Fix: Disconnect non-essential USB devices, test RAM sticks one by one, and if available, use dual BIOS recovery features or reflash BIOS. You may need to replace the motherboard if the hardware is failing.

6. Stuck on “Press F1 to Continue” screen

BIOS halts with this prompt due to detected but unresolvable issues, for example, CMOS checksum errors from a weak battery, improper boot device settings, or fan sensor errors.

Fix: Replace the CMOS battery if the clock resets, set the boot devices correctly, disable faulty fan sensors in BIOS hardware monitoring, and save changes before exiting.

7. BIOS password problems

Lost or forgotten BIOS passwords can lock you out of BIOS settings or prevent system boot.

Fix: Reset the CMOS by removing the battery or clearing the jumper. For branded systems, manufacturer master passwords may be needed, requiring contact with support.

8. Failed BIOS update

A partial or interrupted BIOS update can brick the motherboard or cause boot failure.

Fix: Use the built-in BIOS recovery or Flashback functions, if available, by connecting a USB drive with the correct BIOS file. If this does not work, then, as a last resort, professional reprogramming of the BIOS chips may be necessary.

Additional read: Mistakes to avoid when creating backups

Common BIOS configuration settings and their impact on your PC

Here are some of the system settings you can configure from the BIOS setup:

1. Boot order / Boot priority

Controls which device the PC tries to boot from first (e.g., hard drive, USB, optical drive). Setting your primary OS drive first speeds up boot time and prevents boot failure from incorrect devices.

2. System date and time

Ensures the internal clock is accurate, which affects file timestamps, logs, and security certificates.

3. CPU settings

Includes enabling/disabling CPU cores, hyper-threading, virtualization support, and overclocking. Overclocking usually boosts CPU speed but might increase heat and power usage, which increases the risk of instability if not done carefully.

4. Memory settings

Adjust RAM speed, timings, and enable features like XMP (Extreme Memory Profile) for optimized performance.

5. Power management

Configures system power-saving features, sleep modes, and actions related to power button presses, affecting energy consumption and responsiveness.

6. Security settings

Set BIOS passwords to prevent unauthorized changes, enable Secure Boot to protect boot integrity, and disable unused ports or devices for enhanced security.

7. Integrated peripherals

Enable or disable onboard devices like audio, USB controllers, network adapters, or legacy ports, impacting hardware availability.

8. Fan control and thermal monitoring

Adjust fan speeds and temperature thresholds to balance cooling performance with noise levels.

9. SATA Mode 

Determines how storage drives communicate with the system. AHCI enables modern features like hot-swapping and NCQ, improving SSD performance.

10. Quick boot and POST settings

This enables faster boot by skipping certain hardware tests, but disabling these can help with troubleshooting hardware issues.

Additional read: How to use Windows Command Prompt: The ultimate guide

How to keep BIOS safe?

Due to its low-level access to hardware, BIOS presents a prime target for sophisticated attacks. Hackers can directly target the BIOS to introduce malicious code in the system. In fact, the importance of BIOS security has been highlighted by several notable incidents. 

For example, in a Cylance demonstration, security researchers showed how attackers could manipulate the BIOS to disable crucial security features, allowing malware to survive a complete operating system reinstall. 

Moreover, the Plundervolt attack revealed a vulnerability in Intel's CPUs that allowed attackers to manipulate voltage settings to bypass security protections within the CPU's firmware, clearly showing that even low-level hardware can be a vector for attack. 

Here are some of the best practices you can follow to keep your BIOS safe:

1. Set strong BIOS passwords: Use strong passwords that include uppercase, lowercase, numbers, and special characters. Also, change your passwords periodically and keep them secure.

2. Enable Secure Boot: Secure Boot, a UEFI feature, ensures only trusted, signed bootloaders and operating systems can load during startup, preventing bootkits and rootkits. It also blocks unauthorized or malicious software from running at the boot level.

3. Keep BIOS firmware updated: Regularly check for and apply BIOS updates from your hardware or motherboard manufacturer. Updates include patches for vulnerabilities and improve system security and stability. Use official sources to update the BIOS and follow the vendor's instructions carefully.

4. Restrict physical access: Prevent unauthorized physical access to your computer or motherboard. Use chassis locks or store systems in secure locations since physical access can allow BIOS tampering or resetting of passwords.

5. Configure BIOS to limit boot devices: Set BIOS to boot only from trusted devices, disabling booting from unauthorized USB drives or external media. This reduces the risk of booting from malicious devices.

Additional read: Crank up platform security with password policy, IP whitelisting, 2FA, and more

Final thoughts

From initializing critical computer hardware to handing control over to the operating system, BIOS ensures your system starts smoothly without any hiccups. Just as important is its role as the first gatekeeper of your system’s security. 

Keeping your BIOS secure means following a few best practices: updating firmware regularly, enabling built-in security features, setting strong administrative passwords, and restricting unauthorized access. These steps ensure that the foundation of your system remains stable and uncompromised. 

But in modern IT environments, manual oversight is not enough. That is where platforms like SuperOps can be of great value. With its powerful endpoint management and security capabilities, SuperOps allows IT teams to proactively monitor devices using remote access, automate routine fixes in real time, and enforce compliance from a single, centralized platform, keeping systems secure, efficient, and free from disruptions. 

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