Firmware

Week 5 · Module 5: Firmware · Download .docx

Objectives

Describe UEFI vs legacy BIOS and key advantages of UEFI
Explain POST and identify common failure indicators
Identify the CMOS battery and its function
Configure boot order, Secure Boot, and XMP in UEFI

Key terms

UEFI: Unified Extensible Firmware Interface — modern firmware supporting GPT, Secure Boot, and drives over 2 TB.
POST: Power-On Self-Test — firmware diagnostic run at every boot.
CMOS battery: CR2032 coin cell — keeps BIOS settings and RTC alive when unplugged.
Secure Boot: UEFI feature blocking unsigned bootloaders — required for Windows 11.
XMP: Extreme Memory Profile — one-click BIOS toggle for rated RAM speed.

The concept

At power-on, the CPU immediately executes code from the UEFI firmware chip. The firmware runs POST (verifying CPU, RAM, keyboard, and storage), then hands off to the bootloader. UEFI replaced legacy BIOS in the mid-2010s — it supports GPT (drives over 2 TB), Secure Boot (blocks rootkits), a graphical interface, and network booting. The CMOS battery (CR2032) maintains a tiny amount of non-volatile RAM that stores your BIOS settings and real-time clock. Without it, settings reset every power cycle. Never power off during a firmware flash — partial writes corrupt the BIOS chip and may require professional recovery.

Worked examples

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Common mistakes

Powering off during a BIOS flash — partial write corrupts firmware and can brick the board.
Enabling Secure Boot before verifying the installed OS has a valid signature — the system will refuse to boot.
Forgetting to enable XMP after new RAM installation — system runs at 2133 MHz by default.

Self-check

Try each one before you look. A miss here costs nothing and tells you exactly what to reread.

1. What runs immediately when a PC is powered on?

2. A PC resets clock and BIOS settings every time it is unplugged. Most likely cause:

3. Key advantage of UEFI over legacy BIOS:

4. Secure Boot protects against which threat?

5. Risk of powering off during a BIOS firmware flash:

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