The primary function of an external hard drive is to provide additional storage space for data outside a computer's internal storage system. This portable device offers a convenient way to back up files, transfer data between different systems, and store large volumes of equivalent media, including documents, photos, and videos. External hard drives come in various formats, including HDD and SSD, with varied storage capacities. Their versatile use cases make them an essential tool for individuals and organizations seeking to manage and protect their data efficiently.