Document size vs File Size

[callydonia]

Hi,
I just started using Adobe Photoshop. I created a document using the following settings:
Width - 2 inches
Height - .875 inches
Resolution - 1200 p/i
Mode: RGB Color
Contents - Transparency

I saved the document as Photoshop (psd)
On the lower left size of the screen, I have a Document size of 7.21M/13.8M

However, when I look at my file using Windows Explorer, it is 939KB.

Can someone explain why my file size using Windows Explorer isn't 7.21M or 13.8M?

Thanks.
Cally

 

[blueark]

A PSD file is a compressed file format, so it should be smaller on disk that it actually is. The Document size shows two numbers: The left hand number is the approximate "printing" size if the image was flattened, and extra channels discarded. The right hand number is the actual file size including layers and other information.