When you define a computed field, it becomes:

a$.$

A physical data field that is stored in your project file.

b$.$

A physical field that is stored in your data file.

c$.$

A virtual field that is stored in your data file.

d$.$

A virtual field that is stored in your table layout, within the project file.

e$.$

Both a virtual and physical field because Analytics stores it in memory and also in the data file temporarily for that session only.