RAID protects data by spreading it across multiple hard drives so that if any single drive fails, the data is mirrored by the remaining drives. With NAS, you don't just store your data and forget about it. But the NAS unit doesn't have to be brought down like a typical server whenever data needs to be backed up. Plus, NAS is easy to install. NAS is really a file server approach to storage.
Servers typically provide onboard data processing, and application processing and serving.
The difference is that file serving is all NAS does. The PTO's information must be available at all times for patent and trademark examiners who have research quotas. PTO examiners research applications for patents and trademarks on various types of intellectual property. PTO stores 30 million patent documents on its computer system. That includes all U.S. patent documents back to 1790 plus collections, as well as European and Japanese patents.