GRE general test is a general test as the name suggests and GRE subject test means for a specific subject. However, key differences are in table below and similarities are below it. Please read through and understand.
Major Similarities in GRE general and GRE subject tests are:-
Both tests are part of the GRE series and are used for graduate school admissions.
Both require substantial preparation and understanding of test-taking strategies.
Both tests are scored on a standardized scale to facilitate comparison among applicants.