FDISI           Disable interrupts                   Exceptions: None
FNDISI          Disable interrupts, no wait          C3 C2 C1 C0: [??]

FDISI
FNDISI

        Logic   Interrupt Enable Mask ← 1

    FDISI disables interrupts in the 8087 only. It sets the Interrupt
    Enable Mask (IEM) in the control word, which prevents the 8087 from
    issuing interrupt requests. If WAIT is decoded with pending
    exceptions, the 8087 produces an input (whether masked or not).


    Note
    This instruction disables interrupts in the 8087 only. It is
    recognized but ignored in later FPUs.


    Opcode      Format
    9B DB E1    FDISI
    DB E1       FNDISI


    Timing
    Variations    8087         287        387      486     Pentium
    fdisi         2-8           2          2        3       1      NP
    fndisi        2-8           2          2        3       1      NP

                The wait version may take additional cycles