Macintosh: Explanation of "About This Macintosh..."

When I choose "About This Macintosh..." from the Apple menu, I get information about my computer's memory and how it's being allocated. When I look at how much memory my applications are using, I typically see a grayed bar that's fully or partially filled by a black bar. Sometimes the black bar moves around.

What do the black and grey bars indicate? I have always thought the gray was for how much memory the program had reserved for itself and that the black was how much memory it was currently using.
The total bar (black + gray) equals the amount of RAM allocated to the application, with the black portion indicating the amount of RAM currently used by that application. Technically, the program would have to use the operating system's memory manager for the black portion to be completely accurate, and some programs don't do that. The black portion fluctuates in proportion to actual RAM in use.

Notes:

* Under System 6.0.x, you get the same information with the "About The Finder..." item under the Apple menu.

* Under System 7.x, you can get an "About The Finder..." choice under the Apple menu instead of "About This Macintosh..." by holding down the Option key. When you select this menu item, you'll see the mountain Finder graphic.

* Performa systems display the same information with the "About This Computer..." item under the Apple menu.
Published Date: Feb 18, 2012