[en] The BaBar data acquisition system (DAQ) transports data from the detector front end electronics to short term disk storage. A monitoring application (VMON) has been developed to monitor the one hundred and ninety computers in the dataflow system. Performance information for each CPU is collected and multicast across the existing data transport network. The packets are currently collected by a single UNIX workstation and archived. A ROOT based GUI provides control and displays the DAQ performance in real time. The same GUI is reused to recover archived VMON data. VMON has been deployed and constantly monitors the BaBar dataflow system. It has been used for diagnostics and provides input to models projecting future performance. The application has no measurable impact on data taking, responds instantaneously on the human timescale to requests for information display, and uses only 3% of a 300 MHz Sun Ultra5 CPU