IMPORTANT: The Open Ephys GUI documentation has migrated to a new site – please visit https://open-ephys.github.io for the most up-to-date information.
At the upper left of the main GUI window is a "CPU" meter. This is meant to indicate whether the system is being overloaded by processing demands. (This meters the CPU in your desktop/laptop, NOT the Opal Kelly FPGA inside the Open Ephys system.)
The CPU meter represents the percentage of the available buffer time spent processing data. So, if the buffer is 23 ms long (see "Processing Buffer" below), 100% CPU load means it’s taking an average of 23 ms to process each buffer. This may or may not be correlated with the CPU load in the Windows Task Manager, OS X Activity Monitor, or similar system management tool. If you are using a small buffer size, increasing it may reduce the overall load.
Note that because the CPU meter only knows about the Open Ephys buffer, it is not sensitive to other applications on your system that may be using a lot of CPU. If you are, for instance, doing a lot of closed-loop processing in MATLAB, Julia, Python, etc., those will not be reflected and it is your responsibility to make sure that your system can handle the throughput.
To the right of the CPU and disk-full meters is a time, reported in ms. This time controls (but does NOT precisely present) the size of the buffer that Open Ephys GUI uses to process data. If you click on it, you can change this buffer size, which can either improve your overall processing load or make it faster (if more intense) for low-latency closed-loop work. There are more details at Acquisition board data latency .