Lesson 3: BIOS & CMOS
Chapter 3 study guide: quick notes, multiple-choice check, and short written answers.
1. Quick notes
Annotate and print
Use the tool bar at the bottom of the screen to highlight text, draw, and add sticky notes or text on top of these notes. Then save a PDF with or without your marks.
In the print window, choose "Save as PDF" as the destination. Chrome or Edge gives the best result.
The Boot Process
The sequence of steps a computer goes through when powered on until the desktop is reached:
- Power ON: Power supply starts, CPU calls BIOS.
- POST: Power-On-Self-Test checks hardware.
- Loading OS: Finds OS via Boot Sequence.
- System Configuration: OS kernel loads drivers.
- System Utility Loads: Antivirus, volume control, etc.
- User Authentication: Login screen.
RAM vs ROM
- RAM (Random Access Memory): Volatile. Temporarily stores files you are working on. Content erased when powered off.
- ROM (Read Only Memory): Non-volatile. Permanently stores data even when power is cut off. The BIOS is stored here.
BIOS (Basic Input/Output System)
- A firmware program that tells the CPU what to do when powered on.
- Stored on the ROM on the motherboard, so it doesn't lose data when powered off.
- POST (Power-On-Self-Test): A diagnostic test run immediately after power on to check basic hardware components (CPU, RAM, disk drives).
- 1 short beep indicates the POST was successful. Multiple beeps or no beep indicate a problem.
CMOS
- The BIOS program itself is read-only, so it cannot save custom settings (like date/time, boot sequence).
- These settings are saved on the CMOS (a read/write memory chipset).
- CMOS is volatile, meaning it needs constant power.
- A small CMOS battery on the motherboard provides this power when the computer is unplugged.
- If the battery dies, the time/date become incorrect and settings reset to default.
BIOS/CMOS Reset
A common troubleshooting technique for a computer that doesn't boot is to reset the BIOS settings or CMOS.
- BIOS reset: Changes the configuration back to factory default values.
- This helps fix issues caused by incorrect settings or resets the halt process.
- Yellow button: Found on some motherboards, pressing it resets CMOS settings to defaults (but does not clear passwords).
How to Reset the BIOS Password
If you forget the BIOS password, you can clear it using the motherboard jumper:
- Turn off the computer and disconnect the power cord.
- Remove the Blue jumper from its normal position.
- Reconnect power, start the PC to clear the password, then turn it off again.
- Put the blue jumper back onto its original pins and start the PC.
ROM Types
BIOS is stored on ROM. Over time, ROM technology has evolved to allow easier updates:
- ROM chips: Could not be updated; had to be physically replaced.
- PROM: Programmable ROM.
- EPROM: Erasable Programmable ROM.
- Flash ROM (Flash EPROM): Rewritable non-volatile memory that allows you to securely update the BIOS at home.
BIOS Update
Manufacturers release BIOS updates to fix bugs, enhance security, and improve hardware compatibility.
- Download the BIOS update from the manufacturer’s Driver page.
- Run the downloaded program to flash the new BIOS to the ROM.
- Warning: If the computer loses power while updating, the BIOS will be damaged and the PC will not turn on.
BIOS vs UEFI
| Feature | BIOS | UEFI |
|---|---|---|
| Introduction | Older firmware (1980s) | Newer (2000s) |
| Boot Speed | Slower | Faster |
| Interface | Text-based, simple | Graphical interface with mouse |
| Storage Support | Up to 2.2 TB (MBR) | Larger than 2.2 TB (GPT) |
| Security | Basic features | Advanced security (Secure Boot) |
- Secure Boot: Ensures only trusted and signed OS boot loaders and drivers run, preventing malware.
- LoJack: Security feature in some UEFI to help recover lost or stolen laptops.
Computer Electrical Power
- Voltage (V): The "pressure" that pushes electricity. Devices operate at specific voltages (e.g., 220V for home appliances, 3.3V/5V/12V for PC parts).
- Current (I): The flow of electrical charge, measured in Amperes (A). The more power a device needs, the higher the current required.
- Watt (W): The amount of power consumed. A more powerful device requires more watts.
Power Fluctuation and Protection
- Blackout: Complete loss of AC power.
- Voltage spike: Sudden increase in voltage (very short, nanosecond).
- Power surge: Sudden increase in voltage that lasts longer (3+ nanoseconds).
- UPS (Uninterruptible Power Supply): Has a battery that keeps the computer running for 20-40 minutes when the main power goes off.
- Surge Protector: Helps shield against surges and spikes.
2. Multiple-choice check
Pick an answer to see right or wrong straight away, with a short explanation.
3. Short written questions
Try to answer in your own words first, then open the model answer.