I/O time (Threads View)
Applies to: 
Visual Studio 
Visual Studio for Mac
Note
This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here
These segments in the timeline are associated with blocking times that are categorized as I/O. This means that a thread is waiting for an I/O operation to finish. The thread may have been blocked in an API, or by an I/O-related kernel wait that the Concurrency Visualizer is counting as I/O. APIs such as CreateFile(), ReadFile(), and WSARecv() fall into this group.