The design of a real-time analyser for performing fast Fourier transforms is described. Data are gathered at regular intervals without breaks for servicing the purpose-designed Fourier computer, which is used at the maximum speed permitted by this device. Three DMA devices are used to perform input, output and service of the Fourier computer. Separation of the real and complex parts and bit reversal are carried out by unusual wiring of the DMA devices to achieve the necessary speed with relatively few components.