Type 7651 is a dual-channel FFT software option for Real-time Frequency Analyzer Type 2144. Type 7669 is a single-channel FFT software option for Real-time Frequency Analyzer Type 2143. Both come on 3V2” disks and are loaded using the analyzer’s built-in disk drive. A software key must be installed in the analyzer to allow the program to be run. Type 2144 plus Type 7651 offer identical functions and operation as the Type 2148. Type 2143 plus Type 7669 offer identical functions and operation as the Type 2147.