Oh no! Aaaaaarrrgh!
The dreaded "Sad Mac" was how old Macintosh systems told you that something had gone terribly, deeply wrong.
Although problems which resulted in the Sad Mac could sometimes be fixed with utilities, it often left no option but to reformat the hard drive--or, in some cases, the computer had to be repaired by professionals.
In all my years of using Macs, I've only seen the Sad Mac come up twice, or maybe three times. (And, being a total Mac geek, I was always able to handle the issues without calling professionals.) Fortunately, the Sad Mac was a very rare occurrence.
See the little dots just below the hexadecimal number? When the Sad Mac came up, a row of dots there would flicker rapidly in a pattern. The particular pattern was a reflection of the error which had occurred. I've heard that a handful of the most expert Mac developers and technicians could tell just by looking at the hex number and the flashing row of dots exactly what had gone wrong.
Although the days of the Sad Mac are gone, the concept lives on in the form of the Sad iPod.
One of several nostalgic screenshots from old Macintosh Systems that I'm posting.