Best Answer: Currently, the largest named unit of data measurement is the yottabyte which is (give or take) 1211288155777568604160000 bytes. The largest reachable amount of data is the petabyte or 1100585369600 bytes. The current file system, NTFS, can only address hard drives up to 25 petabytes. Here is the list of all the data unit measurements: bit byte kilobyte megabyte gigabyte terabyte petabyte exabyte zettabyte yottabyte. Source(s):