  Based on the Monte Carlo simulations we have studied the performance of the
HEGRA system of imaging air Cherenkov telescopes (IACTs) in its present
configuration of 4 IACTs as well as in its future final configuration of 5
IACTs. Here we present the results on the basic characteristics of the IACT
system which are used in the standard data analysis procedure, i.e., the
collection areas, the detection rates, the angular resolution, the energy
resolution, and the gamma/hadron-separation efficiency. By comparing several
key Monte Carlo predictions with experimental results it is possible to check
the accuracy of the simulations. The Monte Carlo results concerning
hadron-nuclear showers are tested with the recorded cosmic ray events and the
results concerning photon-induced showers are tested with a large data sample
of gamma-rays observed from BL Lac object Mkn 501 during its high flaring
activity in 1997. Summarizing the simulations and current observations we give
the basic recommendations of using the instrument and the major values of its
sensitivity.

Astrophysics