The capacity of all hard disk drives are measured by the manufacturers using true SI (metric) nomenclature. In this system, there are 1000 units in a kilo, 1000 kilo in a mega, 1000 mega in a giga, and so forth. Computers, however, are not based onthe base-10 arithmetic the SI system is.
As such, the binary approximations are 1024 units in a kilo, 1024 kilo in a mega, 1024 mega in a giga, and so forth. The net result of this discrepancy in systems is that anything counted in SI units will always be larger than if it were counted in computer units.
For example, a 200GB hard drive is actually 200,000,000,000 bytes in size. In computer terms, this is 200,000,000,000/1024 = 195,312,500 kilobytes which is 195,312,500/1024 = 190,734 megabytes which is 190,734/1024 = 186 gigabyes. While it appears that 14 gigabytes dissappeared, nothing is actually is missing.
Understanding that factor, if you find you cannot account for some of the space used on your hard-drive, realize there are hidden system files and folders which you, the user, normally cannot access. Among these are the Recycler and System Volume Information folders. (The former is where anything you delete is stored until you empty the Recycle Bin and the latter is where Windows keeps its files necessary for System Restore. Since these folders can get quite large over time, it is advisable that you empty the recycle bin and restrict the amount of space Windows is given for the System Restore function.
Here’s a small list of HD’s and their real sizes:
GB GiB
20 18.62645149
40 37.25290298
60 55.87935448
80 74.50580597
120 111.758709
160 149.0116119
200 186.2645149
250 232.8306437
320 298.0232239
500 465.6612873
750 698.491931
In fact you’re “losing” roughly 7%.