The Specification of the x86

x86 always holds floating-point numbers in 80 bits.
neither 64 nor 32 bits.
A significand (mantissa) part is only rounded along the rounding precision.
Rounding precision holds 2 bits in x86 FPU control word.
An exponential part is always 15 bits.
Despite this design, x86 is conformity to IEEE 754.