You're running a browser inside a chat app
Slack is built with a technology called Electron, which takes the Google Chrome browser engine and packages it inside the application. When you open Slack, your computer isn't just launching a chat app — it's effectively launching a second web browser, even if you already have Chrome or Firefox open.
This isn't a flaw specific to Slack — it's how all Electron apps work. But it explains why the Slack desktop app has a similar impact on your system as opening a dozen heavy browser tabs, and why the Slack app feels so slow even when you're barely using it.
It's not just the memory
RAM gets most of the attention — Slack can use 1 GB or more — but there are two other effects that make your computer slow down when Slack is open:
CPU load: Slack runs background tasks continuously. Even when you're not actively using it, it's syncing messages, checking for updates, and broadcasting your status. On most computers this runs at 1–5% CPU. That might sound small, but it means your processor can't fully rest, and every other program you're running has less headroom.
Memory pressure: When Slack holds 1 GB of RAM, that's 1 GB less available for everything else. When your browser, design tool, document editor, and Slack are all open, your computer may start using the hard drive as overflow memory — a process called "swapping" — which slows things down dramatically.
Why the Slack app gets slower as the day goes on
If you're wondering why Slack is so laggy by mid-afternoon, this is the likely answer: Slack's memory usage grows over a session, not just at startup. Background caches accumulate, and Chromium holds onto memory it has used without always releasing it. A session that started lean at 9 AM can quietly consume far more by 4 PM. That's when the slowness tends to be most noticeable — and why so many people ask why their computer slows down when Slack is open specifically after a few hours of work.
It hits harder on older or mid-range machines
A machine with 32 GB of RAM barely notices Slack's footprint. A machine with 8 GB feels it every single day. The same 1 GB of RAM represents a small share of one machine's memory and a significant share of another's.
If you're using a mid-range laptop — the kind that companies typically issue, or one bought a few years ago — you're in the range where the Slack desktop app's impact is genuine and daily. Why is Slack so slow on these machines? Because Electron was never designed with memory-constrained hardware in mind.
Three things to try right now
- Quit Slack when you step away. Don't minimize — actually quit it from the menu. This frees the RAM and CPU entirely until you need it again.
- Reduce the number of workspaces you're connected to. Each workspace multiplies memory usage. Sign out of ones you use infrequently.
- Disable hardware acceleration (Preferences → Advanced). This eliminates a GPU subprocess and often reduces both heat and memory use.
If you want a permanent fix
The root cause of why Slack is so slow — and why your computer slows down when Slack is open — is that the Slack app is built on a browser engine. No setting changes that. The workarounds help, but they reduce the problem rather than solve it.
A native Slack client — one built as a real desktop application rather than a web app in a box — doesn't have this problem. msga connects to your Slack workspaces and uses roughly 60–100 MB at idle. Your other apps get their breathing room back.