We investigate properties of the class of compact spaces on which every
regular Borel measure is separable. This class will be referred to as MS.
We discuss some closure properties of MS, and show that some simply defined
compact spaces, such as compact ordered spaces or compact scattered spaces, are
in MS. Most of the basic theory for regular measures is true just in ZFC. On
the other hand, the existence of a compact ordered scattered space which
carries a non-separable (non-regular) Borel measure is equivalent to the
existence of a real-valued measurable cardinal less or equal to c.
We show that not being in MS is preserved by all forcing extensions which do
not collapse omega_1, while being in MS can be destroyed even by a ccc forcing
