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Will change OperandSize from 16-bit to 32-bit if CS.D=0, or from 32-bit to 16-bit if CS.D=1. 67h: AddressSize override. Will change AddressSize from 16-bit to 32-bit if CS.D=0, or from 32-bit to 16-bit if CS.D=1. The 80386 also introduced the two new segment registers FS and GS as well as the x86 control, debug and test registers.
Some Linux distributions, such as Fedora, openSUSE, Arch Linux, Gentoo Linux refer to this 64-bit architecture as "x86_64". Apple macOS refers to 64-bit architecture as "x86-64" or "x86_64", as seen in the Terminal command arch [3] and in their developer documentation. [2] [4]
The aged 32-bit x86 was competing with much more advanced 64-bit RISC architectures which could address much more memory. Intel and the whole x86 ecosystem needed 64-bit memory addressing if x86 was to survive the 64-bit computing era, as workstation and desktop software applications were soon to start hitting the limits of 32-bit memory ...
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.
For instance, Microsoft Windows on x86-64 uses the GS segment to point to the Thread Environment Block, a small data structure for each thread, which contains information about exception handling, thread-local variables, and other per-thread state. Similarly, the Linux kernel uses the GS segment to store per-CPU data.
The FLAGS register is the status register that contains the current state of an x86 CPU.The size and meanings of the flag bits are architecture dependent. It usually reflects the result of arithmetic operations as well as information about restrictions placed on the CPU operation at the current time.
INT is an assembly language instruction for x86 processors that generates a software interrupt. It takes the interrupt number formatted as a byte value. [1] When written in assembly language, the instruction is written like this: INT X. where X is the software interrupt that should be generated (0-255).
Intel x86 CPU family NOP: 1 0x90 [2] 0x90 is the one-byte encoding for XCHG AX,AX in 16-bit code and XCHG EAX,EAX in 32-bit code. In long mode, XCHG RAX,RAX requires two bytes, as it would begin with an REX.W prefix, making the encoding 0x48 0x90. However, 0x90 is interpreted as a NOP in long mode regardless of whether it is preceded by 0x48.