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Why is copying files between Mac and Windows so slow?

Most slow copies between a Mac and a Windows PC have one of two causes: the copy is going over Wi-Fi, or the folder holds thousands of small files. Check which connection the copy uses first, then deal with the small files.

Why this is harder than it should be

  • It’s probably going over Wi-Fi. Even with both computers wired or connected by cable, connecting by computer name can find the Wi-Fi address, and every file crosses the air.
  • Small files are handled one at a time. SMB, the protocol both use, opens, writes and closes each file with separate requests. A folder of thousands of small files spends most of its time waiting. In our tests a Mac took almost four minutes to copy 20,000 small files over SMB on a 10 Gb/s link.
  • Every request is signed. Windows 11 version 24H2 requires SMB signing by default on all connections, which adds work to every request.
  • Files are scanned. Microsoft Defender checks files as they arrive on the PC, and checks each file the first time any program opens it. In our tests, 2,000 small files that Defender hadn’t scanned took 18.8 seconds to copy from a PC to a Mac. The second copy took 1.3 seconds.
  • Finder adds extra files and lookups. It writes hidden .DS_Store files to shared folders and asks for icons and previews as it browses.
  • The link itself can be uneven. On one Windows PC and Mac pair with a 40 Gb/s cable, Windows sent the Mac only 12.0 Gb/s while the Mac sent 24.2 Gb/s back, before any file sharing.
  • The cable link needs its own setup. Sharing over a cable means a new network profile, sharing settings, accounts and an address that starts with 169.254, on both computers.

1. Check which connection the copy uses

On the Windows PC, open Task Manager while the copy runs and choose Performance. Each network adapter has its own graph, so you can see whether Wi-Fi or Ethernet is carrying the traffic. The cable shows as an Ethernet adapter.

If Wi-Fi is busy, the copy found the other computer by its Wi-Fi address. Disconnect, then connect again by the address of the wired or cable connection, not by the computer’s name. Turning off Wi-Fi for a moment also confirms the copy isn’t using it.

2. Share over the cable instead of Wi-Fi

If both computers have Thunderbolt 3 or newer, or USB4, a cable between them gives a direct network link. The Mac calls it Thunderbolt Bridge and Windows shows a new Ethernet connection. Each side gives itself an address starting with 169.254, because there’s no router to hand one out.

On the Windows PC

Share a folder over the cable connection:

  1. Open Settings, choose Network & internet, then choose Ethernet and select the cable’s connection.
  2. Under Network profile type, select Private network. Windows sets new connections to Public, which hides the PC and blocks sharing.
  3. Go back to Network & internet, choose Advanced network settings, then Advanced sharing settings. Under Private networks, turn on Network discovery and File and printer sharing.
  4. In File Explorer, right-click the folder, choose Properties, then the Sharing tab, then Share. Add your account and set it to Read/Write.
  5. Open Terminal and run ipconfig. Note the IPv4 address of the cable’s Ethernet adapter. It starts with 169.254.

On the Mac

Connect to the shared folder:

  1. In Finder, choose Go, then Connect to Server.
  2. Type smb:// followed by the PC’s cable address, for example smb://169.254.20.30, and click Connect.
  3. Choose Registered User and sign in with the PC account’s user name and password. If the PC uses a Microsoft account, use its email address and password, not the Windows PIN.
  4. Choose the shared folder. It opens in Finder.

To copy the other way

Share a folder from the Mac and connect from Windows:

  1. On the Mac, open System Settings, choose General, then Sharing, and turn on File Sharing.
  2. Click the info button next to File Sharing, then Options. Under Windows File Sharing, select your account and enter its password.
  3. In System Settings, choose Network, then Thunderbolt Bridge, then Details. Note the IP address under TCP/IP.
  4. On the PC, type \\ followed by the Mac’s address into File Explorer’s address bar, for example \\169.254.40.50, and sign in with your Mac user name and password.

A yellow dot and “Self-assigned IP” next to Thunderbolt Bridge are normal for a cable link. If Thunderbolt Bridge or the PC’s new Ethernet connection doesn’t appear at all, one of the ports or the cable doesn’t carry Thunderbolt or USB4.

3. Zip folders of small files

One large file moves far faster than thousands of small ones. Compress the folder, copy the archive and unzip it on the other side. On a Mac, Control-click the folder and choose Compress. On Windows, right-click it and choose Compress to, then ZIP File.

If you copy from the Windows PC and can’t zip first, robocopy copies several files at once instead of one at a time. In Terminal on the PC, run:

robocopy "C:\Projects\Site" "\\169.254.40.50\Shared\Site" /E /MT:16

Replace the two paths with your folder and the shared folder on the Mac. /E includes subfolders, and /MT:16 copies 16 files at a time. It doesn’t delete anything in either folder.

4. Stop Finder writing .DS_Store files to shares

This changes a Finder setting. In Terminal on the Mac, run:

defaults write com.apple.desktopservices DSDontWriteNetworkStores -bool true

Then log out and back in. To undo it, run the same command with delete in place of write and without -bool true.

5. Reconnect after sleep, restart or unplugging

A shared folder doesn’t come back by itself after either computer sleeps or restarts, or after the cable comes out. Finder says the server connection was interrupted, and File Explorer shows the share with a red X.

Connect again the same way. On the Mac, Connect to Server lists recent servers. On Windows, the address bar remembers the address. If the other computer’s 169.254 address has changed, find the new one first. For ways to keep a share connected, see shared folder disconnects after sleep.

Signing and security scanning protect your files, so we don’t recommend turning them off to save time.