Why we get less memory space than mentioned in memory devices (HD,USB sticks..)

Many of us often think why we get less memory space in the computer world than mentioned.For instance,in a 4 GB pen drive (USB) we get maximum free space 3.73 GB.
Even in HD of 160 GB we get approx 149 GB.Similar is the case of memory stick and so on....

Let me explain the reason.

It is due to conversion of bytes in to Kilo Bytes(KB),Kilo Bytes in to Mega Bytes(Mb) ,and of course Mega Bytes to Giga Bytes(GB),where the factor is of 1024 ,not 1000.

Ok ,let me explain u clearly this with an example....

Let's take an example of 4 GB USB pen drive where we at max 3.73 GB

4 GB = 4 Giga Bytes =4 * (10 ^9) Bytes =4000000000 Bytes (as 1 Giga = 10 ^ 9)

dividing by 1024 = 39,06,250, Kb (as 1 Kb = 1024 Bytes)

dividing again by 1024 = 3814.7 Mb ( as 1 Mb = 1024 Kb)

dividing again by 1024 = 3.73 Gb

So, finally 3.73 Gb is the maximum we can get.