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A general description is here.
It incorporates (slightly revised) copies of packages ‘multicore’ and ‘snow’ (excluding MPI, PVM and NWS clusters). Code written to use those packages should work unchanged (apart from changing any references to their namespaces to a reference to ‘parallel’).
It also contains support for multiple RNG streams following L'Ecuyer _et al_ (2002), with support for both ‘mclapply’ and ‘snow’ clusters. This replaces functions like ‘clusterSetupRNG()’ from ‘snow’ (which are not in ‘parallel’).
The ‘colormodel’ for ‘postscript()’ which does use both gray and sRGB colorspace is now called ‘"srgb+gray"’.
Plots which are known to use only black/white/transparent can advantageously use ‘colormodel = "gray"’ (just as before, but there is now slightly more advantage in doing so).