# How to see which process is using the most CPU or memory on a Mac > The NotchStar Disk tab, Monitor, Usage shows the five busiest processes by CPU and by memory, refreshed every few seconds. No per app history. Canonical: https://www.notchstar.com/use-cases/see-which-process-is-using-the-cpu-on-a-mac/ Last updated: 2026-11-04 Published 2026-11-04. Open the notch, choose Disk, then Monitor, and leave it on Usage. Two columns list the busiest processes by CPU and the ones using the most memory, five of each. A third column lists listening ports. It refreshes about every three seconds while you look at it. ## Steps 1. Open the notch and choose **Disk**, then **Monitor**. 2. Press **Usage** if Ports is showing. 3. Read **Busiest (CPU)**, which gives each process name and a percentage, and **Most memory**, which gives the memory in a size such as megabytes. 4. Keep the notch open (the **Keep open** button in the header) while you reproduce the problem, such as starting a build or opening a heavy page. 5. Watch which name stays on top. ## Reading the numbers The numbers come from the system's ps tool. The memory figure is resident memory, which is what a process holds in RAM right now. Neither tells you why a process is busy. ## Pair it with the overall gauges The [System tab](https://www.notchstar.com/features/system-stats/) shows total CPU, memory, disk and battery as rings, plus network speed, sampled each second. It answers "is my Mac busy?". The Monitor answers "which process?". Use the gauges first, then Monitor for the name. The [build use case](https://www.notchstar.com/use-cases/watch-cpu-and-memory-during-a-build-on-a-mac/) puts both together. ## Limits - **Top five only.** If the culprit is sixth, you will not see it. - **Snapshots, not history.** There is no graph over time and nothing is logged. - **No per process network or energy figures.** - **No grouping.** Several helper processes of one app appear as separate rows. - **Name only.** It shows no icon and no way to open the app from the row. - **You can stop only listening servers,** from the Ports view. The Usage view has no quit button. - **Sampling stops when you leave the section,** which keeps NotchStar itself quiet. If the busy process is an app you recognise, use that app's own quit. If you do not recognise the name, search for it before you act, since many background processes are part of macOS. The [Disk page](https://www.notchstar.com/features/disk/) explains the other sections, including how to see what a port belongs to. ## Quick answers. ### Is this a replacement for Activity Monitor? No. It shows five processes by CPU and by memory. Activity Monitor shows everything with more detail. ### Does it run all the time? No. It samples only while the Monitor section is on screen. ## Keep reading. - [Disk space, duplicates, apps and cleanup](https://www.notchstar.com/features/disk/): See free space, find big folders, duplicates and app leftovers, compress media and clean caches from your Mac notch. Everything goes to the Trash. - [CPU, memory, disk, battery and network](https://www.notchstar.com/features/system-stats/): Live CPU, memory, disk, battery and network speed gauges in your Mac notch. Sampling only runs while the tab is open, so it stays light. - [How to watch CPU and memory while a build runs on a Mac](https://www.notchstar.com/use-cases/watch-cpu-and-memory-during-a-build-on-a-mac/): Keep the NotchStar System tab open while a build or test run goes, then check Disk, Monitor for the heaviest processes. Totals only, no history. - [How to stop a dev server that is still running on a Mac](https://www.notchstar.com/use-cases/stop-a-dev-server-from-the-mac-notch/): Use NotchStar Disk, Monitor, Ports to find a forgotten dev server and press Stop twice to send a quit request. It never forces a kill. ## More in Coding. - [How to find what is using port 3000 on a Mac](https://www.notchstar.com/use-cases/find-what-is-using-port-3000-on-a-mac/): Open the NotchStar Disk tab, Monitor, Ports, then filter by 3000 to see the command, project folder and whether it is local or on the network. - [How to stop a dev server that is still running on a Mac](https://www.notchstar.com/use-cases/stop-a-dev-server-from-the-mac-notch/): Use NotchStar Disk, Monitor, Ports to find a forgotten dev server and press Stop twice to send a quit request. It never forces a kill. - [How to reuse terminal commands from clipboard history on a Mac](https://www.notchstar.com/use-cases/copy-commands-from-clipboard-history-on-a-mac/): Copy several commands while reading docs, then paste them one at a time from the NotchStar Clipboard tab. Plain text, 50 items, cleared on quit. - [How to free up disk space on a Mac used for development](https://www.notchstar.com/use-cases/free-up-disk-space-on-a-developer-mac/): Scan caches, logs, Xcode DerivedData and old downloads with the NotchStar Disk tab, choose what to move to the Trash, and learn what each item means. - [How to watch CPU and memory while a build runs on a Mac](https://www.notchstar.com/use-cases/watch-cpu-and-memory-during-a-build-on-a-mac/): Keep the NotchStar System tab open while a build or test run goes, then check Disk, Monitor for the heaviest processes. Totals only, no history.