The Apple Macintosh startup sequence is what happens when you turn on or start up a Macintosh.
Sequence
Pre-Mac OS X
Origin
When you attempt to start up a Macintosh 128k, the startup chime plays while the screen is still off. Then the screen fades to gray. If a floppy disk is detected, a Happy Mac icon will appear after a few seconds.
If you wait a few seconds after seeing the Happy Mac, this dialog box will appear:
And then the Electronic Desk (desktop) appears on-screen.
However, if startup fails, you’ll see the Sad Mac screen plastering the desktop and welcome dialog. Here’s an example:
Hands-on: Have you ever booted up a Macintosh 128k? Did you see the Sad Mac icon with the error code? Post in the comments!
If there’s not a floppy disk inserted into the Macintosh, the system will still turn on, but you actually won’t see the Sad Mac crash screen. Instead you’ll get this screen:
This is most commonly known as the “Missing OS” screen, and it has nothing to do with a startup failure.
Mac OS 8 and 9
After turning on, the Macintosh will play the startup chime and display a light gray screen with a colored and updated Happy Mac symbol. Here’s what it now looks like:
The updated Happy Mac Symbol.
Then, instead of the classic welcome message, the “Welcome to Mac OS” dialog box will appear, looking a little bit like this:
Then, it will form a background and switch to say “Starting Up…”.
OS X
The startup chime plays as the screen turns to gray. After a few seconds, the Apple logo will appear.
Then a loading sign will appear, and afterwards a login screen will appear.
In previous versions of OS X, there was no login screen. Login screens for the Mac were introduced in OS X Leopard. Also, the Happy Mac icon was removed.
Computer Central 