describe one type of secondary devices in detail

Mobile Hard disk

As the name implies, a hard disk is a storage product that uses a hard disk as a storage medium and exchanges large-capacity data between computers and it emphasizes portability. Most mobile hard disks use USB, IEEE1394, and other faster transmission interfaces, allowing higher speeds and system data transmission.

Because the hard disk is used as the storage medium, the data read/write mode of the mobile hard disk is the same as that of the standard IDE hard disk. As of 2015, the read speed of mainstream 2.5-inch branded mobile hard disk is about 50-100MB/s, and the writing speed is about 30-80MB/s.

Most of the mobile hard drives on the market are based on standard hard drives, and only a few are based on micro hard drives (1.8-inch hard drives, etc.), but the price factor determines that the mainstream mobile hard drives are still based on standard notebook hard drives.