What is a popular portable storage device known for its built-in connector?

A USB flash drive is recognized as a popular portable storage device that features a built-in connector, allowing users to easily plug it directly into various devices without needing additional cables or adapters. This convenience enhances its portability and makes it user-friendly, as it is compact and often small enough to fit on a keychain.

In contrast, external hard drives, while also portable, typically require an external power source and a separate cable for connection, making them less convenient for quick access. Blu-ray discs and CD-ROMs are disk-based storage media that require a compatible disc drive to read the data, and they do not have any built-in connector for direct access, limiting their portability in comparison to USB flash drives. Thus, the unique design of the USB flash drive with its integrated connector distinctly categorizes it as a favored choice for portable storage.