Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.

I am looking for a word or phrase which can be used in the sentence: It is a rather old, but _________________ technology. The word or phrase should address a technology that is totally investigated, researched in detail, and thoroughly optimised, so there is nothing more to find out or improve.
Most common term I have seen repeatedly and would thus use is, well established. It is rather old, but well-established technology Note as correctly point out by @Chappo below in this case grammar dictates a hyphen is required since it is a compound adjective preceding a noun. 'science can be leading edge or well established' Wiki Technology