The whole point of 80 bits is to have a cushion against error accumulation so that you can have double precision with confidence. The fp stack are all 80 bit.

Here's the reference:

[link|http://212.247.200.167/asm/asm_deformed_us/documentation/masm/mmr61/Chap_05.htm|big link]


FLD/FILD/FBLD Load

Pushes the specified operand onto the stack. All memory operands are automatically converted to temporary-real numbers before being loaded. Memory operands can be 32-, 64-, or 80-bit real numbers or 16-, 32-, or 64-bit integers.