12 trillion bytes = 12E12 bytes / (1024^4 bytes/TB) = 10.9 TB
Physical memory was developed with binary address lines (such should be no surprise). A memory with an 8-bit (1 byte) word length and 16 address lines has a capacity of 2^16 bytes = 65536 bytes. If, for memory sizes, we use 2^10 = 1024 instead of 1000 to redefine the metric prefixes, then we have nice whole numbers. Instead of 65.536 KB, we have a simpler 64 KB. As memory capacities grew, this scheme was maintained: 1KB = 1024 bytes, 1MB = 1024 KB, 1GB = 1024 MB, 1 TB = 1024 GB.
Hard disk drives are not addressed the same way as a memory array, so the standard power of 10 definition of the metric prefixes is used (manufacturers make this clear in the small print). So this is a 12 trillion byte hard drive -- see the calculation at the start of this post. The windows operating system will report its size using the memory array convention.