Multi-PC Sync in Windows Mobile 6.5 via WMDC

Windows Mobile Device Center (WMDC) allowed Windows Mobile 6.5 devices to synchronize personal data, media, and files across multiple desktop computers by utilizing structured sync partnerships. Through this mechanism, a single mobile device could maintain distinct data-sharing agreements with up to two separate PCs simultaneously. This article explains how WMDC established these partnerships, managed multi-computer data conflicts, handled item-level permissions, and maintained sync integrity between home and workplace environments.

The Two-PC Partnership Architecture

Windows Mobile 6.5 inherited the core synchronization architecture of the ActiveSync protocol, which placed a hard system limit of two active PC partnerships per mobile device. Additionally, the device could support one direct over-the-air synchronization partnership with a Microsoft Exchange Server.

When a Windows Mobile 6.5 device was connected to a computer via USB or Bluetooth, WMDC inspected the device's internal partnership table:

  • Guest Connection: If the user chose not to create a partnership, or if the device had already reached its two-computer limit, WMDC operated in "Guest" mode. Guest mode permitted basic file browsing, manual software installation, and device configuration, but disabled automated two-way synchronization of Outlook data (Contacts, Calendar, Tasks, and Notes).
  • Standard Partnership: If an open slot was available, the user could register the PC as an official partner. WMDC assigned a unique identifier (GUID) to the relationship, which was stored in both the desktop's registry and the mobile device's system files.

Establishing Distinct Sync Profiles

WMDC allowed users to selectively choose which data categories synced with which computer, preventing redundant or overlapping sync operations. During the partnership setup wizard, the user could customize data types for that specific PC:

  • Work PC Configuration: A user could configure the primary PC to synchronize work-related PIM (Personal Information Manager) items, such as Outlook Contacts, Calendar, and Tasks.
  • Home PC Configuration: The secondary PC could be assigned exclusively to synchronize Windows Media Player playlists, Internet Explorer favorites, photos, and personal documents.

If an item category was enabled on both computers (such as Contacts on both Home and Work PCs), WMDC synchronized the data bidirectionally. A contact added on the home PC would sync to the Windows Mobile device, and subsequently sync to the work PC upon the next connection.

Conflict Resolution Protocols

Managing updates across multiple PCs introduced the possibility of sync collisions, such as when a calendar event or contact was modified on both a PC and the mobile device between sync intervals. WMDC managed these discrepancies using built-in conflict resolution rules configured within the sync settings of each PC:

  1. Desktop Replaces Device: Changes made on the PC took precedence, overwriting conflicting edits made on the Windows Mobile device.
  2. Device Replaces Desktop: Changes made on the mobile handset took precedence, overwriting the corresponding entry in the desktop's Outlook database.
  3. Manual Prompting: WMDC could pause the sync process and alert the user via a desktop dialog box, prompting them to manually choose which record to preserve.

Because these rules were configured locally per PC, a user could set their primary desktop to override the device while setting their secondary desktop to yield to the device.

Partnership Management and Deletion

When a user needed to pair the Windows Mobile 6.5 device with a third computer, one of the two existing relationships had to be removed. WMDC did not automatically overwrite existing partnerships.

To clear a partnership, the user had to open WMDC, navigate to Mobile Device Settings, select Delete Partnership, and confirm the removal. Alternatively, partnerships could be cleared directly on the Windows Mobile 6.5 handset by navigating to ActiveSync > Menu > Options and deleting the target computer profile. Deleting a partnership severed the synchronization link and stopped automated transfers, but left the previously synchronized data intact on both the device and the host PC.