Estimates of ε-entropy and ε-dimension in the Kolmogorov sense are obtained for a class of causal, linear, time-invariant, continuous-time systems under the assumptions that impulse responses, satisfy an exponential order condition

, and frequency responses satisfy an attenuation condition

. The dependence of ε-entropy and ε-dimension on the accuracy ε is characterized by order, type, and power indexes. Similar results for the discrete-time case are reviewed and compared.