I've found that the RAM usage is more related to the number of charts and the software used to generate the charts, rather than the number of monitors.
For instance, when using TWS charts, the very inefficient Java program used to create the charts uses excessive amounts of RAM for each chart, while better charting software such as Ninjatrader would use substantially less RAM for the same number of charts.
For instance, when using TWS charts, the very inefficient Java program used to create the charts uses excessive amounts of RAM for each chart, while better charting software such as Ninjatrader would use substantially less RAM for the same number of charts.