TIMDLL from http://codeproject.com/ccp/JpmTimers.asp or BOSDLL from http://codeproject.com/ccp/BOS.asp had just this in mind. Both use a MultiMedia timer, it trips a heart-beating thread (every millisecond) which: - 1) spins-a-thread(starting at user supplied entry point), 2) causes a function execution(starting at user supplied entry point) or 3) sets an event-flag as the user has specified. It is accurate to one millisecond. Lymington

It's buffered... up to a point, say, several 10s of K

WinMM.lib gives possibility of one millisecond callbacks on a seperate thread, which one can boost priority to make sure free-running. timeSetTimer & timeKillTimer are the relevant functions, viz. MSDN Better than (+/-) 7mSecs, but perhaps not good enough? Lymington