Invited review abstract

I show results of an analysis of the calculations by Bonnell et al. 2003 and 2008 where between a few hundred and about 2500 stars/sink particles are formed. Via identifying subclusters one can follow quantitatively the time-evolution of structure, mass segregation and the higher-mass initial mass function. I find that the properties of the subclusters depend on their evolutionary stage, with evidence for primordial mass segregation. The upper limit of the initial mass function is not consistent with the generally assumed 150 $M_\odot$ for the physical upper limit, but is increasing with an increasing number of stars that are formed. I will also discuss whether this $n$-dependent upper limit is present in observational data.