What is the BIOS?
BIOS - Basic Input/Output System
When user pressed the power button, the main job of BIOS is let platform to enter operating system.
Where is the BIOS?
The BIOS is stored in flash ROM on the mother board. The ROM size is depended on BIOS binary size.
What is the legacy BIOS? What is the EFI BIOS?
The legacy BIOS is written by assembly code.
The EFI(Extensible Firmware Interface) BIOS is written by C code.
The legacy BIOS is replaced by EFI BIOS little by little.
The EFI BIOS is more easy to write for progarmmer.
How to boot to operating system by the EFI BIOS?
The EFI BIOS has four phases to boot to OS.
1. SEC phase: Check security and cache as RAM in order to build the PEI foundation to provide interface
2. PEI phase: CPU/chipset early initial and most important thing is memory sizing then enter DXE IPL.
3. DXE phase: Execute all the driver in order to let system has full function.
4. BDS phase: Connent all boot device and let system boot to be selected boot device.
System Power On -> SEC -> PEI -> DXE -> BDS -> OS
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何謂BIOS?
BIOS - 基本輸入輸出系統
當使用者按下電源鈕之後,讓系統能順利進到OS,並且達到客製化的需求,這就是BIOS的主要職責。
BIOS放在那裡?
BIOS被存放在主機板上的快閃記憶體內。快閃記憶體的容量大小是取決於BIOS的執行檔大小。
何謂legacy BIOS? 何謂EFI BIOS?
Lgacy BIOS的原始碼是使用組合語言來撰寫。
EFI(Extensible Firmware Interface) BIOS的原始碼是使用C語言來撰寫。
現今,legacy BIOS已漸漸地被EFI BIOS所取代。
EFI BIOS對於程式設計師來說,比較容易看懂,不需要碰到太多硬體底層的程式。
EFI BIOS是如何開機至作業系統的?
EFI BIOS需要經過四個階段的開機流程到作業系統。
1. SEC階段: 檢查系統安全性並將快取記憶體當作記憶體來使用以利建構PEI 環境並轉移至PEI 階段。
2. PEI 階段: CPU/chipset初始化及記憶體初始化讓系統進入到DXE IPL。
3. DXE階段: 執行所有driver為了讓系統能有完整的功能。
4. BDS階段: 連接所有可開機的裝置且讓系統開機到被選中的可開機裝置。
系統Power on -> SEC -> PEI -> DXE -> BDS -> 作業系統