Comment by adrian_b

The 80-bit format was included in the IEEE standard since the beginning.

The IEEE standard had included almost all of what Intel 8087 had implemented, the main exception being the projective extension of the real number line. Because of this deviation in the standard, Intel 80387 has also dropped this feature.

Where you are right is that most other implementers of the standard have chosen to not provide this extended precision format, due to the higher cost in die area, power consumption and memory usage, the latter being exacerbated by the alignment issue. The same was true for Intel when defining SSE, SSE2 and later ISA extensions. The main cost issue is the superlinear growth of the multiplier size with precision, a 64-bit multiplier is not a little bigger than a 53-bit multiplier, but much bigger.

Nowadays, the FP arithmetic standard also includes 128-bit floating-point numbers, which are preferable to 80-bit numbers and do not have alignment problems. However, few processors implement this format in hardware, and on the processors where it would need to be implemented in a software library one can obtain a higher performance by using double-double precision numbers, instead of quadruple precision numbers (unless there is a risk of overflow/underflow in intermediate results, when using the range of double-precision exponents).

In general, on the most popular CPUs, e.g. x86-64 based or Aarch64 based, one should use a double-double precision library for all the arithmetic computations where the traditional 80-bit Intel 8087 format would have been appropriate.