## ALP Programming Guide and Reference

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### Description

FRSTOR reloads the FPU state (environment and register stack) from the memory area defined by the source operand. This data should have been written by a previous FSAVE or FNSAVE instruction.

The FPU environment consists of the FPU control word, status word, tag word , and error pointers (both data and instruction). The environment layout in memory depends on both the operand size and the current operating mode of the processor. The USE attribute of the current code segment determines the operand size: the 14-byte operand applies to a USE16 segment, and the 28- byte operand applies to a USE32 segment. Refer to the Intel documentation for the environment layouts for both operand sizes in both real mode and protected mode. (In virtual-8086 mode, the real mode layout is used.) The stack registers, beginning with ST and ending with ST(7), are in the 80 bytes that immediately follow the environment image. FRSTOR should be run in the same operating mode as the corresponding FSAVE or FNSAVE.