Mario just provided a very nice summary of the difference between stacks and devfiles. Read this and marvel at our continued ignorance and confusion over Che terminology

We should add this disambiguation at least in CRW Releases Notes. Maybe also somewhere to be defined in upstream.

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"The stacks are dead, long live the stacks!"
In Che v6 the stacks were defined in a big stacks.json file that was included with the che-server. That file doesn't exist anymore in Che v7.
In Che v7 the stacks are defined in the devfile registry that is a separate service. And every single devfile in the registry correspond to a stack.
The confusion comes from the fact that in Che v6 stacks and workspaces were defined using 2 different formats. With Che 7 the same format (the devfile) is used to define both.
But a user opening the user dashboard won't notice changes: in Che v7 there is still a list of stacks to choose from as a starting point to create workspace.
I would leave Stacks here because the Devfiles are not "pre-configured workspaces".