# When you buy a new 500 GB hard disk drive, you found that the hard disk capacity as seen in the OS is around 465.7GB. Why?

Relevance
• 1 month ago

There are two reasons for this.  As others have said, vendors often quote on the basis of using decimal sizes instead of binary sizes.

Also, the manufacturers (wishing to 'boost' their product's apparent size quote the raw, unformatted capacity of the disk.  However the OS knows better and tells you the true available disk space after allowing for formatting, directories, etc.

Lv 7
1 month ago

Vendors sell drive sizes by decimal numbers(1000, etc.), not binary (1024). Windows operating systems show disk sizes in binary measurements. So something 1000 in decimal is not quite 1024 binary, and Windows shows it in binary size by converting to binary math. (1000/1024=976.5 corrected to the original 1000 decimal size). This 1024 factor applies to every size step, kilobytes, megabytes, gigabytes,terabytes, etc.

Thus in Windows, 465.7GB is actually 500,000,000,000 decimal bytes (plus a few MB lost to formatting) So, if you multiply 465.7 * 1.024*1.024*1.024, you get close to 500

• 1 month ago

500 Gb is the gross size.  one Mb is actually 1024 Kb or so

• 1 month ago