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x86-64 (also known as x64, x86_64, AMD64, and Intel 64) [note 1] is a 64-bit version of the x86 instruction set, first announced in 1999. It introduced two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level paging mode.
The x86 architectures were based on the Intel 8086 microprocessor chip, initially released in 1978. Intel Core 2 Duo, an example of an x86-compatible, 64-bit multicore processor AMD Athlon (early version), a technically different but fully compatible x86 implementation
The x86 instruction set refers to the set of instructions that x86-compatible microprocessors support. The instructions are usually part of an executable program, often stored as a computer file and executed on the processor.
The term 64-bit also describes a generation of computers in which 64-bit processors are the norm. 64 bits is a word size that defines certain classes of computer architecture, buses, memory, and CPUs and, by extension, the software that runs on them. 64-bit CPUs have been used in supercomputers since the 1970s (Cray-1, 1975) and in reduced ...
On the x86-64 platform, a total of seven memory models exist, [7] as the majority of symbol references are only 32 bits wide, and if the addresses are known at link time (as opposed to position-independent code). This does not affect the pointers used, which are always flat 64-bit pointers, but only how values that have to be accessed via ...
reengineered P6-based microarchitecture used in Intel Core 2 and Xeon microprocessors, built on a 65 nm process, supporting x86-64 level SSE instruction and macro-op fusion and enhanced micro-op fusion with a wider front end and decoder, larger out-of-order core and renamed register, support loop stream detector and large shadow register file.
The x86 processors support five modes of operation for x86 code, Real Mode, Protected Mode, Long Mode, Virtual 86 Mode, and System Management Mode, in which some instructions are available and others are not. A 16-bit subset of instructions is available on the 16-bit x86 processors, which are the 8086, 8088, 80186, 80188, and 80286.
The x86-64 architecture does not use segmentation in long mode (64-bit mode). Four of the segment registers, CS, SS, DS, and ES, are forced to base address 0, and the limit to 2 64. The segment registers FS and GS can still have a nonzero base address. This allows operating systems to use these segments for special purposes.