CompTIA A+: Understanding BIOS and CMOS

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Module 7:

As a CompTIA A+ professional, understanding BIOS and CMOS is essential for configuring and troubleshooting computer systems.

What is BIOS and CMOS?

Let’s delve into these critical components:

BIOS (Basic Input/Output System):
  • BIOS is a firmware that initializes and manages hardware components during the boot-up process. Key aspects to consider include:

  • Boot Process: BIOS performs a Power-On Self-Test (POST) and identifies the boot device (e.g., hard drive, USB, or CD-ROM) to load the operating system.

  • Accessing BIOS: Typically, you access BIOS by pressing a specific key (e.g., F2, Del, or Esc) during the initial boot sequence.

Common BIOS Settings:
  • In BIOS settings, you can configure various aspects of the computer, including:

  • Boot Sequence: Specify the order in which devices are checked for bootable media.

  • Date and Time: Set the system’s date and time, which is crucial for timestamps and file synchronization.

  • Password Protection: Configure BIOS passwords to enhance system security.

  • Hardware Configuration: Customize settings for CPU, RAM, and peripheral devices.

CMOS (Complementary Metal-Oxide-Semiconductor):
  • CMOS is a technology used to store BIOS settings, ensuring they are retained even when the computer is powered off. Key points to understand include:

  • CMOS Battery: CMOS settings are maintained by a small battery on the motherboard, which must be replaced if it loses charge.

  • CMOS Reset: If BIOS settings become corrupted or forgotten, you can reset CMOS to default values by removing the CMOS battery temporarily.

BIOS Updates:
  • Regularly updating BIOS can bring improved hardware support, bug fixes, and security enhancements. It’s important to follow manufacturer guidelines when updating.
Troubleshooting BIOS Issues:
  • As a CompTIA A+ professional, you should be able to address common BIOS problems, such as incorrect boot order, password issues, or corrupted settings.
BIOS in UEFI Systems:
  • In modern systems, Unified Extensible Firmware Interface (UEFI) is replacing traditional BIOS. Understanding the differences and functionalities is crucial.
Best Practices:
  • For A+ professionals, it’s important to document BIOS settings, especially when making changes. This documentation can be invaluable for future troubleshooting.

Accessing BIOS

Below are some of the manufacturers BIOS keys. To enter the BIOS menu, you reboot the system and soon as it begins to boot up to start tapping the key until the BIOS menu appears. If the operating system boots, repeat the process until you reach the BIOS menu instead.

BIOS Manufacturer Keystroke
ACER F2 or delete
Compaq F10 or F2
DELL F2 or delete

Note: There are many more manufacturers with their own ways to enter the BIOS menu.

BIOS/CMOS Settings

If a client has the blue screen of death, you will need to enter the BIOS/CMOS settings.  

When in the BIOS you can check:
  • Processor speeds which is important to know when determining the clock speed or the amount of cache memory present in the processor.
  • Amount of memory, the type of memory and the speed of the memory (also useful when looking to upgrade).

The BIOS allows configuration of:
  • The parallel port. Occasionally when connecting a new device, the parallel port may need configuring in the CMOS.
  • Date and time configuration.
  • Boot sequence configuration.
Advanced settings:

  • Globally unique identifier
  • BIOS date and version number
  • USB ports
  • NIC
  • Virus protection
  • Built-in diagnostics

Understanding BIOS and CMOS is fundamental for configuring and maintaining computer systems. It’s a skill that empowers IT professionals to manage hardware settings effectively and resolve issues that may arise during the boot-up process.

You can find all of our CompTIA A+ guides here:

We also have guides for the CompTIA Security+ here:


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Luke Barber

Hello, fellow tech enthusiasts! I'm Luke, a passionate learner and explorer in the vast realms of technology. Welcome to my digital space where I share the insights and adventures gained from my journey into the fascinating worlds of Arduino, Python, Linux, Ethical Hacking, and beyond. Armed with qualifications including CompTIA A+, Sec+, Cisco CCNA, Unix/Linux and Bash Shell Scripting, JavaScript Application Programming, Python Programming and Ethical Hacking, I thrive in the ever-evolving landscape of coding, computers, and networks. As a tech enthusiast, I'm on a mission to simplify the complexities of technology through my blogs, offering a glimpse into the marvels of Arduino, Python, Linux, and Ethical Hacking techniques. Whether you're a fellow coder or a curious mind, I invite you to join me on this journey of continuous learning and discovery.

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