The Gateway System tags provide status about the system, such as memory usage, performance metrics, and so on. They exist for the Client and the Gateway. You can modify the Gateway System tags to use alarming, history, and scaling but additional System tags cannot be added to the System folder. The tag names and folder structure is managed by the Ignition Gateway.
The Client tags, as the name implies, are only available for use in Clients. They are scoped at the client level unlike the Gateway executed tags. All clients will have the same client tags however the actual values the client tags represent will be independent of each other. In other words even though they are created in the Designer, each client will create their own instances. This makes them very useful as in-project variables, for passing information between screens, and between other parts of the clients, such as scripting.
Client tags do not have a scan class. When set to run as an expression or query, a poll rate is specified dictating how often the value should be calculated.
Client tags support datasets in addition to all the other datatypes such as integers and date-times.