As discussed elsewhere, a trade secret is confidential information deriving independent economic value from being a secret, is not easily discoverable using proper means, and is subject to reasonable secrecy efforts. A patent includes the discovery or invention of a new and useful process, and must be disclosed. Patentable information can be protected as a trade secret. Before a patent application is filed, it starts out as a trade secret. Confidential information protectable as a trade secret can often be patented.
The discovery or invention cannot be both a trade secret and patent. Trade secrets require secrecy, while patents require disclosure. A proprietor of such information must choose one or the other. If the invention or discovery has been on-sale or otherwise in the public for one year, it is no longer patentable. If it is not new and useful, but it derives economic value from being a secret, it is not patentable but is protectable as a trade secret.
Whether to seek patent protection or protect the information as a trade secret is an economic consideration. If your information is likely to be discovered within 20 years by reverse engineering, then you should seek patent protection. If you have a patent and someone reverse engineers it, they are still guilty of patent infringement. You would be able to get damages from infringers and licensing revenue from competitors during the 20-year period.
If you choose not to seek patent protection, and protect the information as a trade secret, it is theoretically protectable in perpetuity. This is much longer than the 20-year period for a patent. That being said, there is risk in that another party can reverse engineer your discovery or invention. Reverse engineering is a proper means of discovering a trade secret, and you would have no recourse against that party.