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Therefore, modern 32-bit x86 operating systems use the LDT very little, primarily to run legacy 16-bit code. Should 16-bit code need to run in a 32-bit environment while sharing memory (this happens e.g. when running OS/2 1.x programs on OS/2 2.0 and later), the LDT must be written in such a way that every flat (paged) address has also a ...
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.
The Intel 80286 had a 24-bit address bus and as such had a 16 MB physical address space, compared to the 1 MB address space of prior x86 processors. It was the first x86 processor to support virtual memory supporting up to 1 GB via segmentation. [19]
The x86 instruction set includes string load, store, move, scan and compare instructions (lods, stos, movs, scas and cmps) which perform each operation to a specified size (b for 8-bit byte, w for 16-bit word, d for 32-bit double word) then increments/decrements (depending on DF, direction flag) the implicit address register (si for lods, di ...
The x86 instruction set has several times been extended with SIMD (Single instruction, multiple data) instruction set extensions.These extensions, starting from the MMX instruction set extension introduced with Pentium MMX in 1997, typically define sets of wide registers and instructions that subdivide these registers into fixed-size lanes and perform a computation for each lane in parallel.
The 16-bit segment selector in the segment register is interpreted as the most significant 16 bits of a linear 20-bit address, called a segment address, of which the remaining four least significant bits are all zeros. The segment address is always added to a 16-bit offset in the instruction to yield a linear address, which is the same as ...
The 64-bit extensions to the x86 architecture were enabled only in the newly introduced long mode, therefore 32-bit and 16-bit applications and operating systems could simply continue using an AMD64 processor in protected or other modes, without even the slightest sacrifice of performance [49] and with full compatibility back to the original ...
The PUSHF and POPF instructions transfer the 16-bit FLAGS register. PUSHFD/POPFD (introduced with the i386 architecture) transfer the 32-bit double register EFLAGS. PUSHFQ/POPFQ (introduced with the x86-64 architecture) transfer the 64-bit quadword register RFLAGS. In 64-bit mode, PUSHF/POPF and PUSHFQ/POPFQ are available but PUSHFD/POPFD are not.