Correct. Later on I say: There are some very specific caveats that MRI makes for concurrent IO. If you have one thread that's waiting on IO (ie. waiting for

Correct. Later on I say: There are some very specific caveats that MRI makes for concurrent IO. If you have one thread that's waiting on IO (ie. waiting for a response from the DB or a web request), MRI will allow another thread to run in parallel.