It is this limited precision that makes it more or less non-deterministic in practice: sequencing operations differently may give results that are bit-wise different, but are close enough given the precision guarantees of floating point numbers. So, on different computers your computations may diverge due to different optimizations applied by the compiler/processor. This was especially true with the x87's 80 bits of precision internally, it may be less likely to happen with SSE floating-point.