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FNSAVE

Saves the current x87 FPU environment—including the register stack, control word, status word, tag word, and other state information—to a specified memory location.

The following table covers what the source and destinations can be.

DO NOT support LOCK

This instruction is available in 32-bit mode and 64-bit mode (compatibility mode). In 64-bit mode, it operates only when the processor is executing in compatibility mode.

The memory destination m108 MUST be 16-byte aligned to avoid potential performance penalties or alignment exceptions depending on the environment. Failure to provide a valid memory address will trigger a general-protection exception (#GP). The instruction does not trigger any floating-point exceptions (#I, #Z, #D, #O, #U, #P).