We currently support real time data retrieval for only Bloomberg and Reuters. There is no technical limit to the number of securities that you can receive updates from.
However, if you have several hundred, then you will most likely see latency in your callbacks, meaning that new data comes in faster than the callbacks can run. In other words, the rate at which callbacks are triggered is greater than the rate at which callbacks can run. This will result in old data being used. Running on an older machine using Bloomberg, the demo callback stockticker with the SP500 Index members falls behind pretty quickly.
