What Actually Happens When You Open an App?
Those two seconds feel instant. They're anything but.
I was in a lecture once, laptop open, phone on the desk. I tapped Instagram out of habit the kind of tap you don't even think about and while it was loading I thought, for the first time: what is actually happening right now? Like, what just occurred between my thumb and that feed appearing? I had no answer. And that bothered me more than I expected.
So I looked into it. And what I found was that those one or two seconds you spend waiting for an app to open are some of the most packed, coordinated moments in computing. There are five or six different systems waking up and talking to each other just so you can scroll. Let's walk through all of it.
First — where does the app actually live?
Before anything else, it helps to understand the difference between two places on your device: storage and RAM. They sound similar. They do very different things.
Fast, temporary working space. Whatever your phone is actively using right now lives here. The moment you close something, it eventually gets cleared to make room for the next thing.
Permanent, slower memory. Your apps, photos, music, everything that stays on your phone when you turn it off is stored here. Larger but much slower to access than RAM.
When you install an app, it sits in storage the filing cabinet. When you open it, the phone has to pull it out of the cabinet and put it on the desk so it can actually work with it. That journey from storage to RAM is the first thing that happens every time you tap an app icon.
What actually happens, step by step
Your tap triggers a whole sequence of events that your phone handles in under two seconds. Here's how it goes:
The touchscreen sensor detects your finger and sends a signal to the operating system — iOS or Android. The OS identifies which icon you tapped and which app it belongs to.
If you opened the app recently, parts of it might still be sitting in RAM from last time. If so, it relaunches almost instantly, this is why some apps open faster the second time. If not, the OS moves to the next step.
The OS fetches the app's core files from internal storage and copies them into RAM. This is often the slowest part — storage is significantly slower than RAM, and larger apps take more time to move across.
Once the app's code is in RAM, the CPU starts running it. It sets up the app's logic, initialises your settings, checks for your login session, and prepares the interface to be drawn on screen.
The CPU hands off the visual work to the GPU. The GPU renders the interface; buttons, images, text, animations — and pushes it to the display. This is why GPU performance directly affects how smooth your UI feels.
Apps like Instagram, Twitter, or WhatsApp don't store all their content on your phone. Once the interface is ready, the app sends a request to a remote server, asking for your feed, your messages, your data. The server responds and the content fills in. This is often what causes that brief moment where the app is open but the content is still loading.
All of that six coordinated steps across your touchscreen, OS, storage, RAM, CPU, GPU, and sometimes a server thousands of kilometres away in roughly the time it takes to blink twice.
Why do some apps open faster than others?
Now that you know the process, this question answers itself. A few things determine app launch speed:
What actually affects how fast an app launches
RAM availability — If your phone is running low on RAM, it has to clear out other apps to make room before loading a new one. This is why a phone with more RAM tends to feel snappier when you're switching between things.
Storage speed — Newer phones use faster storage technology (UFS 3.1, UFS 4.0 on Android; NVMe on iPhones). Cheaper or older devices often have slower storage, which means step 3 — loading the app into RAM — takes noticeably longer.
App size and complexity — A simple calculator loads almost instantly because it's tiny and needs nothing from the internet. Instagram loads more slowly because it's large, pulls remote content, and has a lot of initialisation work to do before it can show you anything useful.
Cold start vs warm start — A cold start is when the app isn't in RAM at all and has to be loaded fresh from storage. A warm start is when the OS kept it partially in memory. Warm starts feel almost instant; cold starts take longer. This is why your phone's RAM size directly affects how everyday usage feels.
What about when the app crashes?
A crash is simply the app hitting a situation its code wasn't written to handle. Maybe it expected data in a certain format and received something else. Maybe it ran out of the memory it was allocated. Maybe a server it was talking to went silent mid-conversation. The OS detects that the app has stopped functioning correctly and shuts it down to protect the rest of the system.
It's not your phone breaking. It's the safety net doing exactly what it was designed to do.
Why does any of this matter to you?
Honestly? You don't need this to use your phone. But understanding it changes how you think about the device in your hand and that's the whole point of this series.
When your phone feels slow, you'll know it's probably a RAM issue, not a sign that the phone is "old." When an app loads instantly the second time, you'll know why. When an app crashes, you won't panic you'll understand what happened and why the phone recovered on its own.
And more importantly, you'll start asking better questions about the technology around you. Not just "is this good?" but "how does this work?" That shift from passive user to genuinely curious is what actually makes you a tech enthusiast. We talked about that last time. This is what living it looks like.
Coming up next in the series
We're keeping this going. Here's what's ahead:
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