PC Boot from BIOS
BIOS Boot
After BIOS load completed, the memory layout as the following table. If a bootable device found, the BIOS copy the IPL(Initial Program Loader) to 0x7c00 and JMP to 0x7c00.
The IPL is the MBR(the 1st sector) of a hard disk.
BIOS Memroy Layout
| Start | End | Size | Description |
|---|---|---|---|
| 0x00000 | 0x9FFFF | 640K | Lower 640K RAM |
| 0xA0000 | 0xBFFFF | 128K | Video RAM |
| 0xC0000 | 0xEFFFF | 192K | Other Device BIOS |
| 0xF0000 | 0xFFFFF | 64K | System BIOS |
Lower 640K RAM Layout
| Start | End | Description |
|---|---|---|
| 0x00000 | 0x003FF | 1K Interrupt Vector |
| 0x00400 | 0x07BFF | User RAM |
| 0x07C00 | 0x07DFF | IPL 512 Bytes |
| 0x07E00 | 0x9FFFF | User RAM, 623104 Bytes(640KB - 0x7e00) |