Real Mode Interrupt/Exception Handling
Real Mode Interrupt Descriptor Table (IDT) Structure
In Real Mode, the Interrupt Table resides in memory starting at location zero. The power-on assertion of reset forces the following values into the IDTR (IDT register):
Base address = 00000000h. IDT starts at location zero.
Limit = 03FFh. IDT size is 1KB.
Each IDT entry (the IDT has a fixed length of 256 entries) contains four bytes of information (hence the length of 1KB):
The first two bytes of the selected IDT entry are loaded into the lower part of the EIP register (i.e., into the IP register) when the related interrupt or exception occurs. The upper 16 bits of EIP is set to zero.
The second two bytes of the selected IDT entry are loaded into the CS ...
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