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                  Stack of 80-bit Data Registers
 
            79 78     63 62                                    0
            ┌─┬─────────┬───────────────────────────────────────┐
     ST     ├─┼─────────┼───────────────────────────────────────┤
     ST(1)  ├─┼─────────┼───────────────────────────────────────┤
     ST(2)  ├─┼─────────┼───────────────────────────────────────┤
     ST(3)  ├─┼─────────┼───────────────────────────────────────┤
     ST(4)  ├─┼─────────┼───────────────────────────────────────┤
     ST(5)  ├─┼─────────┼───────────────────────────────────────┤
     ST(6)  ├─┼─────────┼───────────────────────────────────────┤
     ST(7)  └─┴─────────┴───────────────────────────────────────┘
             │    │          └─ Mantissa
             │    └─ Exponent
             └─ Sign
 
                         Tag Word Format
 
        15                     8  7                     0
        ┌──┬──┬──┬──┬──┬──┬──┬──┐┌──┬──┬──┬──┬──┬──┬──┬──┐
        │TAG7 │TAG6 │TAG5 │TAG4 ││TAG3 │TAG2 │TAG1 │TAG0 │
        └──┴──┴──┴──┴──┴──┴──┴──┘└──┴──┴──┴──┴──┴──┴──┴──┘
 
      TAG──Tag values of Data Register Stack
         00 = Valid
         01 = Zero
         10 = Invalid, infinity, or denormalized
         11 = Empty
 
                        Control Registers
 
                           ┌──────────┐
     Control Word          ├──────────┤   Each word is 16 or 32
     Status Word           ├──────────┤   bits, depending on
     Tag Word              ├──────────┤   segment mode. Total
     Instruction Pointer   ├          ┤   size of state is 14
                           ├──────────┤   bytes in 16-bit mode
     Operand Pointer       ├          ┤   or 28 bytes in 32-bit
                           └──────────┘   mode.
 
     Total size of environment is 94 bytes in 16-bit mode or
     108 bytes in 32-bit mode.
 
     See also: Coprocessor Status Word, Coprocessor Control Word
                                    -♦-