  We present results of 2D3V particle-in-cell simulations of non-relativistic
plasma collisions with absent or parallel large-scale magnetic field for
parameters applicable to the conditions at young supernova remnants. We study
the collision of plasma slabs of different density, leading to two different
shocks and a contact discontinuity. Electron dynamics play an important role in
the development of the system. While non-relativistic shocks in both
unmagnetized and magnetized plasmas can be mediated by Weibel-type
instabilities, the efficiency of shock-formation processes is higher when a
large-scale magnetic field is present. The electron distributions downstream of
the forward and reverse shocks are generally isotropic, whereas that is not
always the case for the ions. We do not see any significant evidence of
pre-acceleration, neither in the electron population nor in the ion
distribution.
