BIOS Technical Interview Questions

What is BIOS?

BIOS stands for Basic Input/Output System. It is a type of primary program that is required for every computer. The BIOS is responsible for managing the data flow between the computer's operating system and the attached devices, such as the monitor, hard disk, video adapter, keyboard, mouse and printer. Without the BIOS, the computer’s microprocessor will not be able to connect, view, or interact with these devices. The BIOS is a ROM chip that is located directly on the motherboard.

What are some functions of BIOS?

BIOS is a significant part of a computer. It’s primary function is to is to boot up the operating system. In order to do it, it must first identify and test all hardware components, such as monitor, keyboard, processor, hard drive, other optical drive, etc. It will then load the operating system and then transfer control to it. Additionally, it will also load the drivers for the hardware components to ensure that the operation system can detect and control them.

What is the sequence of things done by the BIOS when you turn on your Computer?

When the computer is first turned on, the BIOS instructions are initiated. The BIOS will then conduct the following tasks in order:

  1. Enumerates the RAM by checking each compartment to see that they are all working
  2. Then checks for other devices attached to the computer
  3. Detects all the peripherals, including the keyboard and mouse and then checks for the boot options
  4. Checks boot options in the sequence configured on the BIOS. Eg. Boot from CD-ROM, Boot From Hard Drive, Boot from LAN etc.
  5. Checks for bootstraps on the devices as configured on the BIOS
  6. Loads the essential parts of the OS into the RAM, and hands over control

There are a lot of other things that a BIOS does, such as check the CMOS and other chips, and load device drivers into the memory, among other things. However, these are the primary function of the BIOS.

Explain the difference between BIOS and CMOS

BIOS and CMOS are often considered to be the same, or even similar, however, they are not. They are two different components that need to work together to ensure that the computer functions properly. Both BIOS and CMOS are memory chips that are a physical part of the motherboard.

BIOS stands for Basic Input/Output System. It is primarily responsible for containing a special program that loads the computer’s operating system, and helps the computer processor to detect and control the hardware components such as disk drives, video cards, sound cards, network cards, disk drives, ports, USB, hard drives, etc.

The CMOS stands for Complementary Metal Oxide Semiconductor, and it houses the setting configurations. It is powered by the onboard battery. If the battery runs out of power, the CMOS with revert to factory mode.

It the simplest of terms, it is the physical storage device that stores all of the BIOS set-up routines. The setup can be used to change the time and date, as well as how the hardware devices, such as hard drives and disc drives are loaded at start up. The CMOS setup can also be used to enable and disable various hardware devices, such as USB ports, video card, sound card, parallel and serial ports, as well as other devices.

In order for BIOS to do its job, it first reads the information that is stored in the CMOS. The CMOS tells the BIOS what to do with the hardware devices and how to interact with them.

How to reset CMOS or BIOS settings?

The computer stores low-level settings such as the system time and hardware settings in its CMOS. Sometimes it may be necessary to reset the CMOS or BIOS especially if experiencing a hardware compatibility issue or something similar.

There are three main ways to reset CMOS or BIOS settings.

1. Via the BIOS menu

  • Restart the computer.
  • Press the key to enter the BIOS, typically Del, F1, F2, or F10.
  • Wait for the BIOS screen to appear.
  • Find the factory reset option.
  • Select the option or press the button to load your factory defaults.
  • Save changes

2. Use the CLEAR CMOS Motherboard Jumper

  • Shut down the computer and unplug the power cord
  • Open the case and access the motherboard
  • Find the CMOS jumper, which is a three-pin jumper on your motherboard
  • Remove the jumper and move it over to another set of pins
  • Press and hold the power button for 10 to 15 seconds to dispel any electricity remaining in the capacitors (without plugging in the computer)
  • Remove the jumper and move it back to the original position
  • Start the computer

3. Reset the CMOS Battery

  • Shut down the computer and unplug the power cord
  • Open the case and access the motherboard
  • Find the CMOS battery, which is a flat round disk shaped battery
  • Carefully remove it
  • Press and hold the power button for 10 to 15 seconds to dispel any electricity remaining in the capacitors (without plugging in the computer)
  • Wait five minutes before resetting the battery or replacing it if necessary
  • Start the computer, enter your BIOS and reconfigure all of the settings, including the time, date, and boot order.
How do you reset the BIOS password, when you forget it?

If one has forgotten the BIOS password, the only way to reset it is by resetting the entire BIOS or CMOS settings. The ideal way to reset the BIOS or CMOS settings would be to use the BIOS menu to reset it to factory settings; however this cannot be done as it would be impossible to log into the BIOS without the password to access the menu. This only leaves the option of a hard reset.

There are two ways to hard reset the BIOS and CMOS. One it by removing the CMOS Motherboard Jumper and the other is by removing the CMOS battery. Both require the computer to be switched off and unplugged from the power source. One must now open up the case and access the motherboard. Ensure that you are grounded before working on the motherboard so as to avoid damaging the motherboard with static electricity.

Now find and remove either the motherboard jumper or the CMOS battery. Both should be located close to each other. If working with the jumper, remove the jumper from the pins and move it over to another set of pins. Now press and hold the power button without plugging the computer back in to discharge any remaining electricity in the superconductors. Then move the jumper back to its original position and turn the computer on.

Now, if working with the battery, remove the battery, and press and hold the power button. Then replace the battery and turn the computer back on. This will require the reconfiguration of the BIOS settings.

What is the purpose of BIOS?

BIOS is an important part of the computer framework. It primary purpose is to initialize and test the system hardware components, as well as to load a boot loader or an operating system from memory. 

BIOS is usually pre-loaded on to the motherboard. It is typically loaded onto an erasable programmable read-only memory (EPROM) chip. When the computer it turned on, the BIOS is the first thing to boot up. Firstly, it determines whether all of the attachments are in place and are operational. It then loads the operating system from the hard disk to the random access memory (RAM), after which the RAM takes over.

What are the different types of BIOS?

In PCs, some of the most common types of BIOS include the AWARD, AMI, and Phoenix. Some other types of BIOS include:

  • CMOS
  • Syxz
  • Wodj  
What is POST in terms of BIOS?

When a PC is turned on, the first thing the BIOS does is Power On Self Test (POST). At the name indicated, POST is a type of test that is primarily used to diagnose that the BIOS and hardware is running smoothly. Specifically it tests the computer's basic input/output system ability to communicate and control the computer keyboard, random access memory, disk drives, and other hardware.

If the test finds that the BIOS is functioning optimally, then it goes ahead and boots the computer. If it is not, then an error message is displayed on the screen.

Why are POST cards used?

A POST card is type of a plug-in interface card. It is primarily used with BIOS in order to display the progress of a POST. A POST is a Power-On Self-Test, which primarily used to diagnose that the BIOS is running smoothly and is able to communicate with the attached hardware.

In case, the BIOS is not running smoothly, an error message is displayed on the screen.  A POST card is responsible for displaying the error codes that are generated during the POST. It is also used to troubleshoot computers that do not start up.

How does a bootstrap loader work?

Bootstrap loader is a program that is automatically executed by the processor when the computer is turned on. Bootstrap loader is stored in the computer's ROM.
When the computer is turned on, it initially performs the Power On Self Test. When the POST gives out no issues, the Bootstrap loader then loads the operating system for the computer. The operating system then runs and performs its functions.

How to enter BIOS?

The BIOS is the one that loads the operating system. So it is entered just when the computer starts. When the computer starts, in the initial few seconds a screen appears showing keys you need to press to access the BIOS. That screen lasts only a few seconds, so you have to be prompt in selecting the designated key. Once you press that key, you enter the BIOS

What is a BIOS interrupt call?

BIOS interrupt calls are used to pass messages between the BIOS and the operating system or other BIOS client software. The messages request data from BIOS and return the requested data or action to the caller. BIOS interrupt calls are used to perform some functions such as displaying data to the monitor, reading data from keyboard, etc.

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