A folded spectrum is a one-dimensional spectrum that has been reformatted into two dimensions by cutting it into segments of equal length and arranging the segments in sequential order into a two-dimensional array. Folded spectrum analysis in optical processing allows both spatial dimensions of the optical processor to be used effectively and therefore allows a greater number of spectrum elements to be displayed in parallel. The folded spectrum in optical processing is remarkably similar to the fast Fourier transform (FFT) algorithm in digital processing. The similarities unify many processing concepts and give physical and intuitive insights intc the FFT. More importantly, they show how folded spectrum analysis can be extended to more than two dimensions using either optical or other processing technologies. That result promises a rich variety of computing architectures for the immediate future.