A file system that supports only sequential access requires all files to be read or written from the first to the last byte, only. Such access methods are appropriate file files residing on a magnetic tape for example. A file that can be accessed in any order supports random access. An application may read a configuration file that supports random access sequentially. That means that the operating system allows any access pattern, but the application chose to read it sequentially.
Some operating systems allow the contents of a file to be directly encodes as a file type.
How types are encoded in the system and how rigidly type restrictions are enforced control how type-based the file system is. Strongly-typed operating systems require file types to be encoded in every file, and enforce restrictions. As a result files generally have only one function, and their use can be easily controlled. Older business computers, especially mainframes had strongly-typed systems. The advantage is that file use, and the procedures that underly them can be tightly constrained.