Computer Literacy Starts with Developing a Mental Model of Filesystems
November 2019 (perspective of an assistant professor)
To teach computer literacy, first teach how computer filesystems work at a basic level.
I'm not saying everyone needs to know how filesystems are implemented; but everyone does need to learn a mental model that's accurate enough for them to predict what happens as they interact with their favorite apps. Unfortunately this can be really hard to do because GUIs in modern operating systems hide many filesystem details or expose them to users in inconsistent ways.
(But everyone just uses mobile devices nowadays! They don't need to know about filesystems, right? Jump to the end to find out.)
Family Computing Woes
Whenever I visit family for the holidays, I'm the I.T. person in charge of fixing whatever computer problems have piled up over the past few months. But being an HCI/UX researcher, I can't resist first learning about their existing mental models before offering any potential fixes. So I have them walk through what they're trying to do and where exactly they're getting stuck.
Here are four stories from my most recent trip home where I helped a family member who wanted to download, convert, and archive videos.
1. Where does this app place its output files?
First he wanted to use a Mac video converter
to convert videos he downloaded from YouTube (more on this later) into a
format that he could play on his TV. He saw that the app was placing the
converted output video files into a
Remedy: To prevent such confusion, I imagine that an OS-wide monitoring tool (like a taskbar widget) could automatically detect what files were being written by the currently-active app and visualize exactly where those files are located in the filesystem. This could be implemented atop, say, DTrace for macOS.
2. Why is this app taking forever to launch every time?
The next problem he mentioned was that the video converter app took forever to start each time he clicked on its icon in the dock. That was surprising to me, since he had a fast iMac. The dock icon looked normal, but when I clicked on it, it popped up this “Verifying” dialog which did take forever to finish:
This happened time and time again, so it wasn't a one-time thing that
just popped up on the first launch. It wasn't at all obvious what was
going on, but then I noticed that the app's compressed disk
What's going on here is that there are two files within this compressed
disk image: the video converter app (left) and a shortcut to the
However, what he did (which seems perfectly reasonable!) was double-click on the video converter app within the compressed disk image, which uncompressed and launched it. Then he added that running app to the dock, where its icon looks exactly like the app's real icon (because it is!). However, now whenever he clicks that dock icon, he's launching the copy of the app contained within the compressed disk image, which is why it takes forever to uncompress and run that "Verifying" step on it (which may be a recent macOS added security thing) ...
Since this method of 'installing' apps seems to be unique to macOS, I
had to demonstrate the proper mental model of
Remedy: I'm not sure what the best solution is here, but perhaps the
OS should issue a warning when users try to launch an app or add
something to the dock that lives on some other mounted drive (like a
3. How do I install youtube-dl on macOS?
This family member uses macOS on an iMac, but to my surprise he also had Ubuntu Linux installed on a separate PC. He uses Ubuntu for only one app, youtube-dl, to download videos from YouTube. He then transfers those videos to his iMac to convert them to a format that he can later watch on his TV (see above).
He's not a programmer, but he knew that Ubuntu had a built-in terminal app. He was able to successfully follow these installation instructions from the youtube-dl webpage (screenshot taken in Nov 2019) by copying and running these two commands:
He used Ubuntu for this because he didn't know that macOS also had a terminal. When I told him that it did and showed him how to add the terminal to his dock, he was excited that he could ditch Ubuntu entirely and just use his iMac to do everything he needed.
However, when he followed those exact same instructions (which said that it should work on "OS X", an older name for macOS), he saw the following error message on the macOS terminal:
Warning: Failed to create the file /usr/local/bin/youtube-dl: Warning: No such file or directory 0 1711k 0 16360 0 0 4707 0 0:06:12 0:00:03 0:06:09 147k curl: (23) Failed writing body (0 != 16360)
At first glance, it's not at all obvious what the problem is.
The first line hints at not being able to create the file
To debug this issue, I showed him how to break down the path
OK let's take a look at those folders with the macOS Finder app:
Wait, there's no way to get to
The fix was simple:
sudo mkdir /usr/local/bin
(Note that this also requires a mental model of permissions; we must
have sudo privileges to create a folder inside of
One could argue that youtube-dl should've updated its installation instructions to work on the latest macOS, or better yet, provided a one-click installer. But this program was exactly what my family member needed, so he had to learn to work with it, warts and all.
Remedy: Again a DTrace-like
OS-wide monitoring widget could automatically alert the user when a
4. Where does youtube-dl download its files?
Finally, now that youtube-dl is installed, he can run it on the command line to download videos. But where are those videos placed on his computer? This is exactly the same problem as the first story above: 1. Where does this app place its output files?
When he opens a new terminal, it defaults to his home directory
As shown above, he can get to folders like Desktop, Documents, and
Downloads, but not to the home directory! The way to do so is to run
Remedy: Again a DTrace-like OS-wide monitoring tool could automatically alert the user that youtube-dl had created a new file (the downloaded video file) within a certain folder and prompt the user to open it. Ideally such a tool should not only show users the relevant files but also teach them how to form a robust mental model so that they can know what's going on in the future even when such a tool isn't available (e.g., when they're using someone else's computer).
But what about mobile devices?
Now that we're mostly on our mobile devices, do we still need to develop a mental model of filesystems? I would argue yes: Despite the fact that mobile operating systems try to hide filesystems from us, mobile apps are still built on top of them. I think these concepts are even harder to understand on mobile (definitely not easier!), since people are now dealing with distributed filesystems every day due to cloud services and cross-device syncing. When something goes wrong, it's really hard to understand why.
Appendix: Further reading
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Last modified: 2019-11-11