# How to watch CPU and memory while a build runs 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. Canonical: https://www.notchstar.com/use-cases/watch-cpu-and-memory-during-a-build-on-a-mac/ Last updated: 2026-11-04 Published 2026-11-04. Start the build, open the notch, choose System and press **Keep open**. The gauges show CPU, memory and disk as percentages with network speed beside them, sampled once a second. To find which process is responsible, switch to Disk, then Monitor. ## Steps 1. Start the build or test run in your terminal or editor. 2. Open the notch and choose **System**. The rings show CPU, Memory and Disk, plus Battery on a Mac that has one and Network download and upload rates. 3. Press **Keep open** in the header, so the notch stays up while you work in other windows. 4. Watch the colours. Usage turns orange above 65 percent and red above 85 percent. A battery turns red when low and green while charging. 5. If the CPU stays red, choose **Disk**, then **Monitor**, to see the five busiest processes by CPU and by memory. 6. When the build ends, press **Unpin**. ## Time the build Start a stopwatch in [Timers](https://www.notchstar.com/features/timers/) before the build. It keeps counting while the notch is closed, and you read it by opening the notch. When you change something and rebuild, you can compare the two times. It is not a benchmark, since a busy Mac gives noisy results. Run each case a few times and write the numbers down yourself, because the stopwatch keeps no history. ## What the numbers mean Memory is active, wired and compressed memory against your Mac's total. The disk ring is how full the disk is, not how busy. Network speeds come from WiFi and Ethernet, and VPN or other virtual interfaces are left out so traffic is not counted twice. The first network reading appears after the second sample. ## Limits - **Totals only.** The System tab has no per app breakdown. - **No graph or log.** You see now, not what happened five minutes ago. - **Not a profiler.** It will not tell you why a compile is slow. - **Temperature and fan speed are not shown.** - **Per core load is not shown.** - **Pinned means in the way.** A pinned notch sits above other windows at the top of the screen, so unpin it when done. For deeper work use Instruments or Activity Monitor. These gauges are for a glance. See the [System page](https://www.notchstar.com/features/system-stats/) for the full list. ## Quick answers. ### Does the System tab show which app is using the CPU? No. It shows totals. Use Disk, Monitor, Usage to see the busiest processes. ### Does watching make my Mac slower? It reads a few system counters once a second, only while the tab is on screen. ## Keep reading. - [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. - [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. - [How to see which process is using the most CPU or memory on a Mac](https://www.notchstar.com/use-cases/see-which-process-is-using-the-cpu-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. - [Timer, stopwatch and Pomodoro in the notch](https://www.notchstar.com/features/timers/): A timer, stopwatch and Pomodoro with session tracking, always one hover away in the Mac notch. It keeps counting while the notch is closed. ## 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 see which process is using the most CPU or memory on a Mac](https://www.notchstar.com/use-cases/see-which-process-is-using-the-cpu-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. - [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.