Resource Cheatsheet
A+ Core 1 3.5: The BIOS
A+ Core 1 3.5 — BIOS firmware, POST and boot, legacy BIOS vs UEFI, dual-BIOS flash, and safe setting changes.
- Updated
- Reading time
- 3 min read
- Detail
- A+ Core 1
- Detail
- The BIOS
On this page
In one line: the BIOS is the motherboard firmware (now in flash) that runs POST, hands off to the bootloader, and — as modern UEFI — gives a consistent, graphical setup for devices, CPU, power, security and boot.
Companion to: Professor Messer A+ Core 1 (220-1201), Section 3, objective 3.5. The full version is the BIOS class notes; the section overview is the Section 3 sheet.
What it is
| Term | Meaning |
|---|---|
| BIOS | Basic Input/Output System — the board’s firmware |
| Other names | Firmware, system BIOS, ROM BIOS |
| Stored in | Flash on the motherboard (not ROM — updatable) |
| Settings/clock kept by | Battery-backed memory (CR2032 coin cell) |
| Dual BIOS | Main + backup chip → recover a failed update |
Boot sequence
Power on -> BIOS/UEFI -> POST -> Bootloader -> Operating system- POST (Power-On Self-Test): checks CPU, memory, keyboard/mouse; error on failure.
- Bootloader: POST passed; loads the OS (may prompt which OS).
Legacy BIOS vs UEFI
| Legacy BIOS | UEFI | |
|---|---|---|
| Age / status | 25+ years, older systems | Modern standard (from Intel) |
| Interface | Text, keyboard only | Graphical, mouse |
| Consistency | Varies | Similar across manufacturers |
| Hardware | Built for legacy hardware; may not support new | Supports modern hardware |
| Partitioning* | MBR (≤2 TB, 4 primary) | GPT; enables Secure Boot + TPM |
*Beyond this lesson, but the practical reason the choice matters at install time.
UEFI settings you’ll see
CPU/firmware overview · connected devices (storage, audio, network) · advanced (CPU features, virtualisation VT-x/AMD-V) · power · security · boot/startup.
- Some settings are critical — back up and document before changing anything, so you can revert.
🔐 Security notes
- Firmware runs below the OS, so a bootkit/UEFI implant survives a disk wipe and reinstall. Keep Secure Boot on, flash only vendor-signed images; dual BIOS aids recovery.
- Lock the boot path against evil-maid access: set a supervisor/UEFI password and restrict boot order so it won’t boot removable media by default. Pair with full-disk encryption.
- Change control is security: an undocumented change (Secure Boot off, boot order opened) quietly weakens a machine — track firmware version and settings in the baseline, and patch firmware (microcode fixes ship this way).
Practice drills
1. What does BIOS stand for, and where is it stored today?
Basic Input/Output System; in flash memory on the motherboard (not ROM).
2. What does POST do?
Power-On Self-Test — checks core hardware (CPU, memory, keyboard/mouse) and shows an error if something core fails.
3. What is the bootloader, and what does reaching it tell you?
The stage that loads the OS (sometimes offering a choice) — reaching it means POST passed.
4. Why do some boards have two BIOS chips?
A main and a backup, so a failed or interrupted BIOS update can be recovered.
5. How is a legacy BIOS navigated, and how does UEFI differ?
Legacy is text-based, keyboard only; UEFI is graphical and mouse-driven, and consistent across manufacturers.
6. What does UEFI stand for and who created it?
Unified Extensible Firmware Interface; created by Intel.
7. What should you do before any BIOS change or update?
Back up and document the current configuration so you can revert — some settings are critical to stability.
Key takeaways
- BIOS = firmware in flash; runs POST, then the bootloader loads the OS.
- Dual BIOS (main + backup) makes updates recoverable.
- Legacy = text/keyboard, older hardware; UEFI = graphical/mouse, modern, consistent, Secure Boot.
- Back up and document before changing critical settings.
- Security: firmware sits below the OS — bootkits survive reinstalls; lock boot order, set a firmware password, keep Secure Boot on, flash only signed images.