Western Digital's SanDisk brand today unveiled a prototype flash drive, which it says is the world's highest capacity USB drive featuring total of 4TB of storage.

Equipped with a USB-C connector, the flash drive is a prototype and thus it's not yet for sale. A 4TB USB-sized flash drive would be prohibitively expensive as even 2TB flash drives cost upwards of $1,000, but it does demonstrate advances in storage technology.

SanDisk is also launching new portable SSDs and a new SanDisk Flashback service for cloud backups. The SanDisk Extreme Pro Portable SSD is designed to offer 1GB/s transfer speeds and it features IP55-rated durability. Set to be released in spring 2019 in 500GB, 1TB, and 2TB capacities, pricing information is not yet available for the Extreme Pro.

SanDisk's Flashback service is available for two of SanDisk's USB drives, the SanDisk Ultra Flash Drive and the SanDisk Ultra Fit Flash Drive. Flashback offers a cloud backup option that creates an online copy of USB drive content so consumers can view, search, and share files even if their drive is lost or in another location.

Along with these products, under its WD brand, Western Digital is introducing a new My Passport Go with 500GB to 1TB of SSD storage.

The My Passport Go features a built-in USB-A cable and transfer speeds of up to 400MB/s, with the SSD protected by a durable rubber bumper. Western Digital has not provided specific release and pricing details for the new My Passport Go.