Discrepancy Between Reported Capacity and Actual Capacity
Many customers are confused when their operating system reports, for example, that their new ST3500620AS 500-GB hard drive is reporting only 465.76 GB in usable capacity. Several factors can come into play when you see the reported capacity of a hard drive. Unfortunately there are two different number systems used to express units of storage capacity:
The storage industry standard is to display capacity in decimal. Even though in binary you have more bytes, the decimal representation of a gigabyte shows greater capacity. In order to accurately understand the true capacity of your hard drive, you have to know which base unit of
measure (binary or decimal) is being used to represent capacity.
Motivation for Proposed Prefixes for Binary Multiples
Once upon a time, computer professionals noticed that 1024 or 210 (binary) was very nearly equal to 1000 or 103 (decimal) and started using the prefix "kilo" to mean 1024. That worked
well enough for a decade or two because everybody who talked kilobytes knew that the term implied 1024 bytes. But almost overnight a much more numerous "everybody" bought computers, and the trade computer professionals needed to talk to physicists and engineers and even to ordinary people, most of whom know that a kilometre is 1000 metres and a kilogram is 1000 grams.
|Two Different Measurements Systems|
|Binary Value |
when two or more people begin discussing storage capacity, some will refer to binary values and others will refer to decimal values without making a distinction between the two. This has caused much confusion in the past. In an effort to end this confusion, all major hard drive manufactures use decimal values when discussing storage capacity.
the Start menu on the bottom left of the screen (it may simply be a Windows logo). Open Computer, right-click on the drive in question, choose Properties.
Windows XP / 2000 / NT
From Windows Explorer, right click on a drive letter, then click on Properties. This shows capacities in bytes, MB, and GB.
Windows 98 / Me
From Windows Explorer, right click on a drive letter, then click on Properties. This shows bytes, MB, and GB.
DOS Prompt ? CHKDSK shows bytes
DOS Prompt ? FDISK shows MB
From the Desktop, click Go on the top menu bar, choose Utilities, choose Disk Utility. Then hold down the Control key and click on the hard drive in question on the left, then choose Information (see the 1st image). The total capacity is listed as bytes and in GB, calculated as binary (see the 2nd image, and note the capacity circled in red).
Much of this information is available from the National Institute of Standards and Technology at http://physics.nist.gov/cuu/Units/binary.html