Why 500gb HDD is 465gb, 8gb flash drive is 7.3 and so..?

This was a question that many of my friends asks me after buying a new Pen drive or memory card. So, here I’m going bring answer the way I told my friend.

All Hard Disk manufacturer way of counting space is different from the way a software count a space. This means to a Hard Disk Manufacturer, 1GB is 1000 MB, 1 MB is 1000 KB and so on.
But actually Software or computer language recognize a space in terms of power of 2 say 21, 22,23 etc. hence a KB is 210 Bytes which is 1024 Bytes not 1000Bytes.

Lets do a little math:
From a Manufacturer a 500 GB hard disk is
500 x 1000 x 1000 x 1000 = 500000000000 Bytes

From the Computer Language point of view a 500000000000 Bytes is:
500000000000/(1024*1024*1024) = 465.6612873077392578125 GB

Now you’ll see why your 500GB hard disk has only less than 500 GB space in total. Well if you go with higher or lower space like 1 TB or 8 GB and so on the space is missing.