A 1TB hard drive is a disk drive that can hold 1 terabyte of data. The first 1TB hard drive was the Deskstar 7K1000, which was produced in 2007 by Hitachi Global Storage Technologies and sold for $399.
A 1TB hard drive is equal to 1 trillion bytes or 1,000GB. The drive is useful for those who store gaming data and have high-performance PCs. Starting in 2014, the drives are produced to use the mSATA form factor.
One terabyte is not the largest hard drive size available, as of June 2015. HGST Western Digital started producing a 6TB hard drive that is filled with helium, in 2013.