You may notice that hard drives always have less space than advertised once they’re formatted. The reason for this difference lies in the way hard drive manufacturers advertise their devices, versus the way Windows computers actually uses the storage devices.
Hard drive manufactureres count one KB as 1000 bytes
Windows counts one KB as 1024 bytes
Therefore a 500gig Hard Drive in Windows shows as approx. 465Gig
while a 4 Terrabyte hard drive will appear as only 3.63 Terrabytes in Windows.
Click on the START BUTTON and then click on THIS PC in Windows 8 or COMPUTER in Windows 7 and then right click on your hard drive and select PROPERTIES as in the above picture.
As you can see the hard drive CAPACITY is actually 4,000,650,883,072 bytes while Windows formats this as only 3.63 Terrabytes.
Which means you do actually have a 4 terrabyte hard drive but Windows reads it as 3.63 Terrabytes.