The short answer
After a macOS update, including macOS 27, your Mac rebuilds its Spotlight index (mds_stores), re-analyses your photos (mediaanalysisd, photoanalysisd), catches up on iCloud sync (bird, cloudd, fileproviderd), downloads new system assets (mobileassetd) and often makes a large Time Machine backup (backupd). That work can make it slow and warm for a day or two. Open Activity Monitor, sort by % CPU, and match the top process to the list below. If it's one of these, leave the Mac plugged in and idle and it settles on its own. If it's still slow after two days, check memory pressure, free disk space and any app that hasn't been updated for the new macOS.
On this page
First, see what's using the CPU
Open Activity Monitor (in Applications → Utilities), choose the CPU tab and click the % CPU column so the busiest process is at the top. Or in Terminal:
top -l 2 -o cpu -n 15 -stats pid,command,cpu,timeThen find the top names in the table below. Most slowdowns in the first days after an update come from one of these.
What's running after an update
| Process | What it's doing | How long |
|---|---|---|
mds_stores, mdworker_shared | Rebuilding the Spotlight index, so search works with the new system. See mds_stores. | Hours, longer with a full disk |
mediaanalysisd, photoanalysisd | Re-reading your photo library with new analysis models. See mediaanalysisd. | Hours to a few days |
bird, cloudd, fileproviderd | Checking iCloud Drive and other synced files against the cloud. | Minutes to hours |
mobileassetd | Downloading new system assets such as voices, dictionaries and on-device models. | Depends on your connection |
backupd | Backing up the changed system files with Time Machine. See backupd. | One large backup |
kernel_task | Slowing busy apps down so the chip can cool while all of the above runs. See kernel_task. | Falls as the work finishes |
mds_stores,mdworker_shared- What it's doing
- Rebuilding the Spotlight index, so search works with the new system. See mds_stores.
- How long
- Hours, longer with a full disk
mediaanalysisd,photoanalysisd- What it's doing
- Re-reading your photo library with new analysis models. See mediaanalysisd.
- How long
- Hours to a few days
bird,cloudd,fileproviderd- What it's doing
- Checking iCloud Drive and other synced files against the cloud.
- How long
- Minutes to hours
mobileassetd- What it's doing
- Downloading new system assets such as voices, dictionaries and on-device models.
- How long
- Depends on your connection
backupd- What it's doing
- Backing up the changed system files with Time Machine. See backupd.
- How long
- One large backup
kernel_task- What it's doing
- Slowing busy apps down so the chip can cool while all of the above runs. See kernel_task.
- How long
- Falls as the work finishes
Most of this waits until the Mac is idle and runs faster on power, which is why a Mac you use all day can stay slow for longer than one you leave alone for an evening.
What to do in the first two days
- Plug the Mac in and leave it idle and awake for a few hours, or overnight with the lid open. That lets the indexing and analysis finish.
- Restart once after the update has finished installing. It clears anything left over from the installer.
- Update your apps. Open the App Store and install every update, then update apps from other sources. Older versions may not be ready for the new macOS yet.
- Check that Time Machine has finished its first backup after the update before judging speed.
Still slow after two days?
If none of the processes above are busy any more and the Mac is still slow, look at memory, disk space and heat.
Memory
memory_pressure | tail -1
sysctl vm.swapusageIn Activity Monitor's Memory tab, a yellow or red memory pressure graph means your apps need more memory than the Mac has, and macOS is using swap on the disk. Quit the apps you aren't using, especially browsers with many tabs, and check for an app whose memory keeps growing.
Disk space
Spotlight, Photos and macOS itself need free space to work. If the startup disk is nearly full, everything slows down. See what's taking up space on your Mac.
Heat
pmset -g thermIf this reports a CPU speed limit or a thermal warning, the Mac is too warm and macOS is slowing it down. Make sure the vents aren't covered and let the background work finish.
Login items and old extensions
Open System Settings → General → Login Items & Extensions and turn off anything you don't need at startup. Software that installs system extensions, such as some VPNs, antivirus and audio tools, may need its own update for the new macOS.
The faster way: Diagnose in iKnowMyMac
iKnowMyMac reads the last hour of your Mac's history and ranks what's behind a slowdown, with the evidence for each cause and one suggested action. After an update it tells you in plain words that Spotlight is re-indexing or Photos is analysing your library, so you know whether to wait or act.