A hardware system for investigating Intersymbol Interference (ISI) in an optical data storage system has been designed and constructed by the author. The system consists of a pattern generator which produces data patterns of variable lengths and bit rates to be recorded on the optical disk. Data marks of the readback signal are quantized by a light-speed clock-counter system, and transferred in parallel to a personal computer for analysis. SNR values for collected data are obtained by computing mark size deviations of the readback signal from the original marks. A pseudo-random pattern of 31 bits is used for calculating SNR values for different spot sizes. Finally, Additive Interleaving Detection (AID) technique is implemented to compute another set of SNR values. 3-5db SNR improvement is observed when AID technique is used.