The 4TB hard drive that was installed and formatted by the TwinStore was a:

Seagate ST4000DM000BOX 4TB 5900rpm, 64MB, SATA 6Gb/s, NCQ

The information is the exact information appeared on the box package cover.

One point worth noting, after the TwinStore formatted the drive (a multiple beeps), I had to switch the TwinStore off and re-boot before Control:PC show correctly the 3.92TB storage space. Before the re-boot, TwinStore indicated 0 GB storage space.

Hope the information is useful.

Happy Listening