Pair PCs with Mouse Without Borders and Know Its File Limits
Learn the four-PC pairing flow, 100 MB single-file limit, unsupported folder transfers, and SYSTEM service risk.
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Pair up to four PCs with a security key
Mouse Without Borders is an input-sharing feature in Microsoft PowerToys. It lets one PC’s keyboard and mouse work across other Windows computers; Microsoft documents support for up to four computers. Enable the utility on each PC. On the first computer, choose New Key. On the second, enter that key and the first computer’s name, then select Connect. Repeat for the remaining PCs. After pairing, move the pointer past a screen edge to switch computers, and arrange the device layout to match the physical monitor positions.
Transfers are one file at a time, up to 100 MB
Clipboard and file sharing are convenient, but file transfer has specific limits. Microsoft lists a 100 MB maximum for a single file. Copy/paste and drag/drop do not support folders or multiple files, and drag/drop does not work with network files. To move a group of files, zip them into one archive that stays within the limit, send it only between trusted PCs, then inspect the received archive and contents before extracting. Check that the transfer is allowed by the policies for both computers.
Enable the SYSTEM service only when needed
Ordinary input sharing is different from controlling the lock screen or elevated applications. Microsoft says Use Service runs Mouse Without Borders under the SYSTEM account so another PC can control those screens, and explicitly warns that this adds security risk. Try normal desktop use without the service first. Consider enabling it only when lock-screen or elevated-app control is necessary and both PCs are trusted and managed. Run PowerToys as administrator to enable it; use Uninstall Service when it is no longer needed.
Diagnose a connection that fails or drops
- Confirm all computers are connected to the same network.
- Recheck the host name and security key, then inspect the device layout.
- Check whether Windows Firewall blocks the connection and review the Mouse Without Borders firewall rule.
- If a connection drops, confirm network connectivity and select Refresh connections.
A security key alone does not establish that every network is safe. Check organizational policy before linking a work PC to a personal device, and limit clipboard and file sharing to what the workflow needs.
Expert context and sources
PCWorld’s 2018 hands-on report describes the productivity benefit of moving one keyboard and mouse between PCs. Use current Microsoft documentation for today’s transfer limits and service security behavior.