Which of the following is NOT a valid file system format used in operating…

Concept

A file system format is the logical scheme an operating system uses to organize, name, store, and retrieve data on a storage device. To answer a "which is NOT a real format" question you must recognize the set of standard, documented file-system formats and spot the fabricated name that does not belong to it.

Application

Compare each listed name against the file systems that are actually documented and supported by operating systems:

• NTFS — the New Technology File System, the default journaling file system of modern Windows.

• exFAT — Extended FAT, designed by Microsoft for flash drives and SD cards that exceed FAT32 limits.

• FAT32 — the 32-bit File Allocation Table, widely used for removable media and cross-platform compatibility.

• ReFS — the Resilient File System, used on Windows Server for data-integrity and large-volume workloads.

• FAT84 — not a documented file-system format anywhere; the real FAT family is FAT12, FAT16, and FAT32. There is no "FAT84".

Cross-check

Four of the five names appear in standard operating-system documentation as working file systems, while FAT84 cannot be found in any authoritative specification or comparison. Since the question asks for the name that is NOT a valid file-system format, the fabricated FAT84 is the one that does not belong.

Result

FAT84 is not a valid file system format.