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. 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.
Lets do a little math:
From a Manufacturer a 250 GB hard disk is
250 x 1000 x 1000 x 1000 = 250000000000 Bytes
From the Computer Language point of view a
250000000000 Bytes is:
250000000000/(1024*1024*1024) = 232.83 G Now you’ll see why your 250GB hard disk has only less than 232.83 GB space in total. Well if you go with higher space like 500 GB and so on the space missing is increasing.