> was working in a space where fast inverse square root was the difference between the program working and it not working Pentium 3 released in January 1999. T

> was working in a space where fast inverse square root was the difference between the program working and it not working Pentium 3 released in January 1999. That CPU, along with all newer ones, support SSE which has RSQRTPS instruction, faster, also much more precise approximation. AMD had it before, PFRSQIT1 / PFRCPIT2 in 3DNow from 1998. Quake 3 Arena released in December 1999. The point of using that approximation is running on older hardware, like Pentium and Pentium 2.