Historian, short term, 90 day, and long term historian. Long term historian is on a separate computer, OPC connection used to communicate the values. A DVD archiving device.
• Because of the volume of data stored, many systems incorporate a data compression algorithm. Reduces the number of data points in the historical database by not repeatedly storing the point if it doesn't change by some small
value. All points are usually reported at some interval even if they don't change.