How to Speed Up macOS Big Sur (11) on a Mac That's Stuck on It

A 2013 MacBook Air handed to me last month had 11.7.10 — the final Big Sur point release — and was struggling to open Safari. The hardware was fine. The OS, after five years of accumulated state, was the problem.

If your Mac doesn’t support newer macOS versions, Big Sur is where you live. Here’s how to make it tolerable in 2026.

What Big Sur is and isn’t

Big Sur (macOS 11) was the redesign release. It moved to the new icon language, brought Apple Silicon support, and overhauled Control Center. It’s also the last supported macOS for several 2013–2015 models, including:

• MacBook Air (2013–2015)
• MacBook Pro 13” (2013–2015)
• MacBook Pro 15” (2013–2015)
• iMac (2014, late 2015)
• iMac Pro (2017) — supports later but many users stayed
• Mac mini (2014)

Apple stopped shipping security updates for Big Sur in late 2024. You’re now running an unsupported OS, which matters for a few things below.

Step 1: Verify you’re on 11.7.10

Apple menu → About This Mac. If you’re on 11.0–11.6.x, update to 11.7.10 — the last public release. Earlier versions had bugs that 11.7.x fixed, and there’s no reason to hold back at this point.

System Preferences → Software Update.

Step 2: Activity Monitor pass

Restart, wait two minutes, open Activity Monitor. Sort CPU descending.

The Big Sur-era suspects:

• mediaanalysisd — Photos analysis. Will finish overnight.
• mds_stores — Spotlight reindex. Below.
• kernel_task — thermal throttling. Critical on older laptops with worn thermal paste.
• WindowServer — high values mean transparency, animation, or external monitor load.
• bird / cloudd — iCloud Drive sync.
• corespeechd — Siri / dictation. If you don’t use either, disable.
• nsurlsessiond — Mail or App Store fetching. Usually transient.

If kernel_task consistently sits at 200%+ on a quad-core, you have a thermal problem, not a software problem. Address it physically: clean fans, check that vents aren’t blocked, use a hard surface instead of a couch cushion, replace thermal paste if the Mac is more than 4 years old.

Step 3: Trim login items aggressively

System Preferences → Users & Groups → Login Items.

On a 4GB or 8GB Big Sur Mac, every background app costs perceptible performance. Cut anything you don’t use within five minutes of starting work:

• Adobe Creative Cloud (you don’t need it running unless you’re actively using a Creative Cloud app)
• Microsoft AutoUpdate (update Office manually a couple times a year)
• Dropbox / Google Drive (close while you work)
• Spotify (open when you want to listen, quit after)
• Slack
• Zoom
• Any printer / scanner helpers you installed years ago

You can always re-add. Start aggressive, see what breaks, re-enable as needed.

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Step 4: Browser choice matters more here than anywhere

On a 4GB or 8GB Mac running Big Sur, browser choice is probably the single biggest variable.

• Safari 16.x (the latest Big Sur supports) is the most memory-efficient. Use it as your daily driver if you can.
• Chrome 116 is the last version to support Big Sur. It still works but it’s a year behind security updates. RAM-heavy.
• Firefox ESR still supports Big Sur with security updates as of early 2026. Reasonable middle ground.
• Brave / Arc / Edge — most have dropped Big Sur support.

For a Big Sur user, the best combination is: Safari for daily work, Firefox ESR for sites that don’t render right in old Safari. Don’t use Chrome unless you must — both because it’s RAM-hungry and because it’s no longer getting updates on Big Sur.

Step 5: Cache cleanup

The Big Sur cache offenders:

• Xcode DerivedData if you ever built iOS projects
• Browser caches in ~/Library/Caches/ per-browser
• Slack in ~/Library/Application Support/Slack/Cache/
• Spotify in ~/Library/Caches/com.spotify.client/Data/
• Mail Envelope Index if Mail is slow
• Old iOS backups in ~/Library/Application Support/MobileSync/Backup/
• Photos thumbnails inside the Photos Library package

Quit the app first, drag the cache to Trash, empty Trash.

For the iOS backups specifically: if you’ve been using this Mac since 2015 to back up phones, you likely have 50GB+ of stale backups. Open the folder, sort by date, keep one or two recent backups, delete the rest. macOS does not auto-clean these.

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Step 6: Reduce visual effects

On older GPUs (Intel Iris, Iris Pro, HD Graphics 5000–6000), this is meaningful:

• System Preferences → Accessibility → Display → Reduce motion: on
• System Preferences → Accessibility → Display → Reduce transparency: on
• System Preferences → Dock & Menu Bar → Minimize windows using: Scale effect
• System Preferences → Dock & Menu Bar → uncheck Animate opening applications
• System Preferences → Mission Control → uncheck Group windows by application if Mission Control is slow

Reducing transparency alone gives you 10% or more GPU time back on Iris-class graphics.

Step 7: Storage — under 15% free is the killer

System Preferences → Storage. Total free space matters more than the breakdown. If you’re under 15% free, the Mac will feel slow no matter what else you do.

Easy wins for clearing space:

• Empty Downloads folder (sort by date, anything older than a month likely doesn’t matter)
• Delete the Trash
• Move your iPhoto/Photos library to an external drive if it’s big
• Delete old iOS backups
• Remove Xcode if installed and not used (15GB+)

Step 8: Spotlight reindex if needed

If mds_stores is hammering disk for hours:

sudo mdutil -E /

Let it finish. Then exclude folders Spotlight doesn’t need: video archives, Xcode build outputs, big media drives.

Step 9: Reset NVRAM and SMC

NVRAM (all Intel Macs):

1. Shut down.
2. Press power, immediately hold Option+Cmd+P+R for 20 seconds.

SMC varies by model. For most 2013–2015 laptops with non-removable battery:

1. Shut down.
2. Hold Shift+Control+Option+Power for 10 seconds.
3. Release, boot normally.

For 2018+ T2 Macs, the procedure is different (search for your specific model). These reset a lot of low-level state and fix surprising issues.

Step 10: Consider an external SSD if your internal is a 5400rpm or Fusion drive

The 2014 iMacs and 2014 Mac minis came with Fusion Drives or 5400rpm spinners. The HDD portion is the bottleneck.

Booting from a USB-C or Thunderbolt SSD turns those Macs into reasonable machines. A $40 1TB external SATA SSD via USB-C, install Big Sur on it, boot from it. The internal becomes Time Machine.

This isn’t ideal long-term, but for a Mac you don’t want to replace yet, it’s a meaningful boost for under $50.

Security caveat: Big Sur is no longer supported

Apple stopped shipping security updates for Big Sur in 2024. That means:

• Don’t use this Mac for online banking or any account that holds money.
• Don’t open suspicious email attachments — your malware protection is frozen at 2024 levels.
• Be cautious about installing new third-party software; many vendors have dropped Big Sur support too.

A Big Sur Mac is fine for writing, browsing trusted sites, photo organization, and general home use. It’s not the right machine for high-stakes online work in 2026.

When to retire it

If you’ve cleaned up and the Mac is still slow:

• Check if a $40–60 external SSD upgrade is feasible.
• Check if you can install OpenCore Legacy Patcher, which lets some Big Sur-only Macs run newer macOS versions unofficially. This is unsupported and can break, but it works for many users.
• Otherwise, this Mac has had a good run. A 2015 MacBook Air served eleven years. That’s a good machine.

The cleanup steps above will buy you another year or two of comfortable use on most Big Sur-supported hardware. After that, hardware limits start to dominate.