  The covariant and non-covariant Quantum Molecular Dynamics models are applied
to investigate possible relativistic effects in heavy ion collisions at SIS
energies. These relativistic effects which arise due to the full covariant
treatment of the dynamics are studied at bombarding energies E$_{lab.}$ = 50,
250, 500, 750, 1000, 1250, 1500, 1750 and 2000 MeV/nucl.. A wide range of the
impact parameter from b = 0 fm to b = 10 fm is also considered. In the present
study, five systems $^{12}$C-$^{12}$C, $^{16}$O-$^{16}$O, $^{20}$Ne-$^{20}$Ne,
$^{28}$Si-$^{28}$Si and $^{40}$Ca-$^{40}$Ca are investigated. The full
covariant treatment at low energies shows quite good agreement with the
corresponding non-covariant approach whereas at higher energies it shows less
stopping and hence less thermal equilibrium as compared to the non-covariant
approach. The collisions dynamics is less affected. The density using RQMD
rises and drops faster than with QMD. The relativistic effects show some
influence on the resonance matter production. Overall, the relativistic effects
at SIS energies ($\leq$ 2000 MeV/nucl.) are less significant.
