BIOS vs UEFI

🧠 BIOS vs UEFI

Feature	BIOS (Basic Input/Output System)	UEFI (Unified Extensible Firmware Interface)
📅 Introduced	1980s	2005+ (modern standard)
🚀 Boot Mode	Legacy (MBR-based)	Modern (GPT-based)
📦 Firmware Type	16-bit, runs in real mode	32-bit or 64-bit, runs in protected mode
🖥️ Interface	Text-based, no mouse support	Graphical + mouse support
💽 Drive Support	≤ 2 TB (MBR limitation)	> 2 TB (GPT support)
🚨 Boot Speed	Slower	Faster
🛠️ Config Storage	Stored on CMOS (battery-backed RAM)	Stored in a special EFI partition on disk
🔄 Secure Boot	❌ Not supported	✅ Supported
💻 OS Compatibility	Older systems (e.g., DOS, Windows 7)	All modern OSes (Windows 8+, Linux, macOS)

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🔧 What They Do (in Simple Terms)

Function	Description
Power-On Self Test (POST)	Hardware check during startup
Bootloader initiation	Finds and loads the OS bootloader
Hardware initialization	Prepares CPU, memory, and devices
System configuration	User can configure boot order, time, etc.

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🎯 Key Differences

🔸 1. Boot Process

• BIOS uses the Master Boot Record (MBR) at the start of the disk to load the bootloader.

• UEFI reads a special EFI system partition (ESP) and loads .efi boot files.

🔸 2. Security

• UEFI supports Secure Boot, which blocks unsigned or malicious bootloaders.

• BIOS offers no boot-time security features.

🔸 3. Extensibility

• BIOS is hardcoded and harder to update.

• UEFI is modular and allows third-party extensions and firmware updates.

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📚 Real-World Analogy

BIOS	UEFI
Like an old Nokia phone — reliable but basic	Like a modern smartphone — advanced, secure, flexible

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🧠 Interview-Ready Summary:

BIOS is the older firmware interface that initializes hardware and boots the OS using a simple MBR-based method. UEFI is its modern replacement, offering faster boot, support for large drives, Secure Boot, and a richer UI via the EFI partition and .efi files. UEFI is now the standard on almost all modern machines.