[Boost-users] question about Boost naming

I am using Boost test library now and find there are several libraries there: libboost_unit_test_framework-mgw46-1_47.a libboost_unit_test_framework-mgw46-mt-1_47.a libboost_unit_test_framework-mgw46-s-1_47.a what are differences between the 3 libraies (with "s", or with "mt", or no "mt" and "s")? also, for VC++ compiler, there is: boost_unit_test_framework-vc100-mt-1_47.dll but MinGW have: libboost_unit_test_framework-mgw46-mt-1_47.dll libboost_unit_test_framework-mgw46-1_47.dll Why MinGW have more?