I know and BIOS knows i have a 120GB hard drive but Win XP (SP2) begs to differ and says i have a 114GB hard drive. Any ideas anybody?

Hi Elskie,

That's the difference between decimal and binary.

Hard drive manufacturers define a megabyte as 1,000,000 bytes and a gigabyte as 1,000,000,000 bytes. That's decimal.

Most system BIOS (not yours I guess) and Windows define a megabyte as 1,048,576 bytes and a gigabyte as 1,073,741,824 bytes. That's binary.

Hard drive manufacturers say a GB is a billion bytes. This is also known as a decimal gigabyte.

When Windows looks at your hard drive, it says that a GB is made up of 1024 MB which is in turn made up of 1024 KB which is in turn made up of 1024 bytes. This is also known as a binary GB.

So:
120 GB (decimal) = 120,000,000,000 bytes
120,000,000,000 bytes / 1024 = 117,187,500 KB
117,187,500 KB / 1024 = 114,440.92 MB
114,440.92 MB / 1024 = 111.76 GB (binary)

It seems to me that your hard drive is actually a little bigger than 120 decimal GB.

114 GB (binary) * 1024 = 116,736 * 1024 = 119,537,664 * 1024 = 122,406,567,936 bytes... or about 122.4 GB (decimal).

And welcome to the forums. :)


Steve beat me to the punch. Also, another of our members, pop pop, has a quote in his signature that's appropriate here: "There are 10 kinds of people in the world: those who understand binary, and those who don't." :D)

Are you sure the size is not being reported by windows as 114,000 MB rather than 114 GB.

120,000,000,000 bytes = 120 GiB = 111.8 GB = 114,441 MB

It is a great and consistent cause of confusion.

Thanks for the help guys.

I do understand binary (passed the A+ hardware test a few months back) but it didnt occur to me that my hard drive size would be displayed in decimal and binary. My hard drive is 122GB but is being displayed as 114GB. One word comes to mind... D'oh!