In Power BI first we get source data. And then we add multiple query steps to filter data/remove column/etc. Then we add relations and model the data.
We can have calculated columns that are stored in the data. And measures that are not stored in the data but calculated on the fly.
Which data is stored in Power BI - the one after query or the one after modelling?
Power BI has 3 connection types for data access. They are import, direct query and live connections. If we use import method as a connection type, data imported into Power bi file using Power BI desktop. So all the data always stays in disk. When query or refresh, data stays in computer memory.This data we can use to query and modeling. After work, we save the Power BI file it will save as file with .pbix extension. Data compressed and stored inside this file.
in direct query mode , data stays in remote location and we can connect data. each time we refresh or make change in slicer request goes to data source and bring back data to power bi. In this method, we can't access data but we can create data model.
live connection is another method. It only support for few data sources. In this method, data not stored in computer memory and can't create data model using Power BI desktop.
Power BI is very well documented. Many of the questions you've recently asked are answered in that resource, so please take a look. I get the feeling that you are using this community because you don't want to read the manual. I strongly suggest you take a look at the documentation, because everything we write in answer to your questions has already been written and documented, and SO is not meant to be a shadow user guide for well documented systems.
Depending on the data source you use in Power BI Desktop, Power BI supports query folding, which will do as much processing of the data at the source (for example SQL Server).
If query folding is not possible because the source does not support it, then the source data is loaded before the query steps are applied.
Read more about query folding here: https://docs.microsoft.com/en-us/power-bi/guidance/power-query-folding
When you perform additional modelling after the Power Queries are loaded, i.e. creating tables with DAX, adding columns, etc., these will be performed when the PBIX file is published to the Power BI service, and they will be performed each time the data is refreshed with the data gateway.
