computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...

, the reset vector is the default location a

central processing unit A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, an ...

will go to find the first instruction it will execute after a reset. The reset vector is a

pointer Pointer may refer to: Places * Pointer, Kentucky * Pointers, New Jersey * Pointers Airport, Wasco County, Oregon, United States * The Pointers, a pair of rocks off Antarctica People with the name * Pointer (surname), a surname (including a list ...

address An address is a collection of information, presented in a mostly fixed format, used to give the location of a building, apartment, or other structure or a plot of land, generally using political boundaries and street names as references, along ...

, 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 Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data. Non-volatile memory typ ...

initialized to contain instructions to start the operation of the CPU, as the first step in the process of

booting In computing, booting is the process of starting a computer as initiated via Computer hardware, hardware such as a button or by a software command. After it is switched on, a computer's central processing unit (CPU) has no software in its ma ...

the system containing the CPU.

Processors

* The reset vector for the

8086 The 8086 (also called iAPX 86) is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-bit data bus (allo ...

processor is at physical address FFFF0h (16 bytes below 1 MB). The value of the

CS register The 8086 (also called iAPX 86) is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-bit data bus (al ...

at reset is FFFFh and the value of the IP register at reset is 0000h to form the

segmented address x86 memory segmentation refers to the implementation of memory segmentation in the Intel x86 computer instruction set architecture. Segmentation was introduced on the Intel 8086 in 1978 as a way to allow programs to address more than 64 KB ...

FFFFh:0000h, which maps to physical address FFFF0h. * The reset vector for the

80286 The Intel 80286 (also marketed as the iAPX 286 and often called Intel 286) is a 16-bit microprocessor that was introduced on February 1, 1982. It was the first 8086-based CPU with separate, non- multiplexed address and data buses and also th ...

processor is at physical address FFFFF0h (16 bytes below 16 MB). 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 Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. The mode gets its name from the fact that addresses in real mode always correspond to real locations in memory. Real mode is characterized by a 20-bit s ...

. This was changed to allow sufficient space to switch to protected mode without modifying the CS register. * The reset vector for the

80386 The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistors PowerPC PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple– IBM ...

Power ISA Power ISA is a reduced instruction set computer (RISC) instruction set architecture (ISA) currently developed by the OpenPOWER Foundation, led by IBM. It was originally developed by IBM and the now-defunct Power.org industry group. Power ISA ...

processors is at an effective address of 0x00000100 for 32-bit processors and 0x0000000000000100 for 64-bit processors. * The reset vector for m68k Architecture processors is 0x0 for Initial Interrupt Stack Register (IISR; Not really a reset vector and is used to initialize the stack pointer after reset.) and 0x4 for initial program counter (reset). * The reset vector for

SPARC SPARC (Scalable Processor Architecture) is a reduced instruction set computer (RISC) instruction set architecture originally developed by Sun Microsystems. Its design was strongly influenced by the experimental Berkeley RISC system developed ...

version 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.

References

Central processing unit Instruction processing {{compu-eng-stub

Processors

See also

References