What does an application check first to determine how to manage a file when prompted to open it?

The process by which an application determines how to manage a file when prompted to open it primarily involves reading the file header. The file header contains critical information about the file, including its format and the specific type of data it contains. This information is essential for the application to understand how to interpret the data properly and decide how to handle it.

The file extension can provide clues about what type of application might be able to open the file, but it is not definitive. Similarly, while the end-of-file marker may denote where the file content ends, it does not dictate how to process the file initially. The $MFT (Master File Table) is relevant primarily in the context of NTFS file systems, detailing the metadata about files, but it is not the first point of reference for applications opening files.

The file header is the authoritative source for the application as it contains the necessary metadata that tells the application the kind of file it is dealing with and how to interpret or render it effectively. Understanding this concept is critical for working with file management and systems that require accurate data handling.