Is there a difference between Boost's scoped mutex and WinAPi's critical section?

The current version of boost::mutex uses neither a Win32 CRITICAL_SECTION, nor a Win32 Mutex. Instead, it uses atomic operations and a Win32 Event for blocking waits.

Older versions (boost 1.34.1 and prior) were a wrapper around CRITICAL_SECTION on Windows.

Incidentally, the mutex itself is not scoped. The boost::mutex::scoped_lock type and, in recent versions, boost::lock_guard<boost::mutex> and boost::unique_lock<boost::mutex> provide RAII wrappers for locking a mutex to ensure you don't forget to unlock it.

The boost::lock_guard<> and boost::unique_lock<> templates work with any type with lock() and unlock() member functions, so you can use them with inter-process mutexes if desired.