The SSE2 extensions to the x86 architecture debuted when the Pentium 4 was released. SSE is a vector processing extension which only dealt with single-precision floats. SSE2 supports double-precision floats. What this means is that as of the Pentium 4, the x86 finally has a sane FPU architecture (the x87 is horrible to program for; it is stack-based, but only has a depth of 7 cells so you get the disadvantages of registers together with the disadvantages of a stack).
What I'm wondering is how widespread Pentium 4 (and above) chips are, and if the x86 backend of the Factor compiler should require SSE2 for floating point operations.
If you have thoughts, share them in the comments. Most likely, nobody will respond, and I will go ahead with my evil plan to drop support for Pentium III chips and older :-)