Recently on Twitter, tech historian Marcin Wichary posed an open question: Why does the Mac screenshot shortcut, Shift+Command+3, start with 3? Why not start with 1 or 2?

As it turns out, as far back as 1984 with the release of the original Mac, Shift+Command+1 ejected the internal (first) floppy disk, and Shift+Command+2 ejected what was then the second (external) floppy disk if one was attached. Here’s a selection from the original Macintosh manual describing it.

Originally, the Macintosh keyboard did not include distinct function keys (such as F1-F12 on an IBM PC), so Apple included a way to simulate them by pressing Command+Shift+1 through Command+Shift+9. Using a system called “FKEYS,” it was possible for people to install custom actions linked to these function shortcuts using the System software folder.

So where did Shift+Command+3 come in? At some point—possibly around System 2.0 in 1985—Apple added a few special FKEY shortcuts to Mac OS that allowed users to capture screenshots as MacPaint files. Wichary discovered Shift+Command+3 described in the Macintosh II manual, released in 1987. Here’s a description of how it works from that manual:

You’ll notice that Apple calls the Command key the “Apple” key here since older Mac keyboards included both a Command symbol and an Apple symbol on that particular key as a holdover from earlier Apple computers. Interestingly, at the same time, Shift+Command+4 output the contents of the active window to a connected printer, sort of like a Mac version of Print Screen.

What Does Shift+Command+1 Do Today?

At some point, Apple changed Mac OS so that Shift+Command+1 no longer ejected disks (if we had to guess, probably around the time Macs got rid of floppy drives in the late 1990s).

Since then, a number of different Mac programs stepped in and began using the Shift+Command+1 shortcut, such as showing the “Photos and Audio” sidebar in Final Cut Pro or selecting all layers in Corel Painter. But it no longer has an official function in macOS.

Instead, if you want to eject a mounted disk, select it in Finder and press Command+E or select File > Eject in the menu bar. And if you need to take a screenshot, press Shift+Command+3 on your keyboard, and you’re all set.