- You can only see the front ~half of the computer in this image. There's yet more computer behind the screen and keyboard. (This photo is a side view that makes it more obvious.)
- Much of that volume is taken up by the sealed lead-acid battery.
- Yes, that means this computer was heavy as fuck. It was nicknamed “the Luggable” for a reason.
- The trackball could be swapped out for a ten-key. Of course, System 6 was impossible to use without a mouse, so that meant you had to plug an external mouse into the ADB port.
- The initial model didn't have a backlight—if you could read the screen in ambient light, great; if not, too bad. A later model added the backlight. (All PowerBooks had it, but some PowerBooks' displays sucked for different reasons.)
From “Guide to the Macintosh Family Hardware”, a detailed and official specification of the innards of various Macintosh models up through 1990, when the book was published. AFAIK this is the last time Apple ever published details on the workings of its machines to this book's level of detail (even getting into specific chips and their relationships).