The resetvector is the default location a central processing unit will go to find the first instruction it will execute after a reset. The reset vector is a pointer or address, where the CPU should always begin as soon as it is able to execute instructions. The address is in a section of non-volatile memory initialized to contain instructions to start the operation of the CPU, as the first step in the process of bootingthe system containing the CPU.
The reset vector for the 80286 processor is at physical address FFFFF0h. The value of the CS register at reset is F000h with the descriptor base set to FF0000h and the value of the IP register at reset is FFF0h to form the segmented address FF000h:FFF0h, which maps to physical address FFFFF0h in real mode. This was changed to allow sufficient space to switch to protected mode without modifying the CS register.
The reset vector for the 80386 and later x86 processors is physical address FFFFFFF0h. The value of the selector portion of the CS register at reset is F000h, the value of the base portion of the CS register is FFFF0000h, and the value of the IP register at reset is FFF0h to form the segmented address FFFF0000h:FFF0h, which maps to the physical address FFFFFFF0h in real mode.
The reset vector for PowerPC/Power ISA processors is at an effective address of 0x00000100 for 32-bit processors and 0x0000000000000100 for 64-bit processors.
The reset vector for SPARCversion 8 processors is at an address of 0x00; the reset vector for SPARC version 9 processors is at an address of 0x20 for power-on reset, 0x40 for watchdog reset, 0x60 for externally initiated reset, and 0x80 for software-initiated reset.
The reset vector for MIPS32 processors is at virtual address 0xBFC00000, which is located in the last 4 Mbytes of the KSEG1 non-cacheable region of memory. The core enters kernel mode both at reset and when an exception is recognized, hence able to map the virtual address to physical address.
The reset vector for the ARM family of processors is address 0x0 or 0xFFFF0000. During normal execution RAM is re-mapped to this location to improve performance, compared to the original ROM-based vector table.
