X86-64: Difference between revisions

Long mode extends general registers to 64 bits (RAX, RBX, RIP, RSP, RFLAGS, etc), and adds an additional 8 integer registers (R8, R9, ..., R15) plus 8 more SSE registers (XMM8 to XMM15) to the CPU. Linear addresses are extended to 64 bit (however, a given CPU may implement less than this) and the physical address space is extended to 52 bits (a given CPU may implement less than this). In essence long mode adds another mode to the CPU:.

Long mode does not support hardware task switching or virtual 8086 tasks, and most of the segment register details are ignored (a flat memory model is required). In long mode the current CS determines if the code currently running is 64 bit code (true long mode) or 32 bit code (compatibility mode), or even 16-bit protected mode code (still in compatibility mode). Using paging has become mandatory, and segmentation has been stripped down for performance reasons.