What is the STG file format?
An .stg file is a proprietary binary backup created by the Backup/Restore wizard in Microsoft ActiveSync versions 3.x through 4.1. When a Windows Mobile or Pocket PC device was connected to a Windows XP PC running ActiveSync, the wizard could dump the device's entire data - contacts, calendar entries, e-mails, photos, application data, and system settings - into a single .stg file.
The format is entirely undocumented. Microsoft never published a specification, and no third-party tool has successfully reverse-engineered it for general-purpose extraction. The only supported way to restore an .stg file was using ActiveSync 4.0 or 4.1 on Windows XP; ActiveSync 4.2 removed the Backup/Restore feature entirely, and neither its successor (Windows Mobile Device Center for Vista/7) nor any current tool reads .stg files.
As a result, .stg files represent a stranded data format: any personal data archived before 2006-2007 is effectively inaccessible without a period-accurate Windows XP installation running ActiveSync 4.0 or 4.1. Microsoft's Backup File Restorer utility (KB article 4220) is no longer available from official download sources.
ActiveSync was superseded by Windows Mobile Device Center (2007) for Vista and Windows 7, and the Windows Mobile platform was discontinued in favour of Windows Phone 7 (2010). No version of the .stg backup format was carried forward to any successor platform.
Security & safety
RISK: LOWSTG files are passive binary backups from an obsolete platform. The format is not an active malware vector. Caution: searching for 'STG file opener' may surface fake utilities - no real modern openers exist.
Format details
in a nutshell- SmartGen genealogy software backup - SmartGen (genealogy application) uses .stg extension for its data backup files.
- Secure Token Generator key file - Some security token and two-factor authentication tools use .stg for stored key data.
Programs that open STG files
Windows1 app
Microsoft ActiveSync 4.0 / 4.1 (legacy)
Free Requires Windows XP. Install ActiveSync 4.0 or 4.1, connect your device (or use the Backup Restore wizard standalone), and restore the STG file. Note: URL may no longer be active on Microsoft servers. Technical details
deep spec| Encoding | Binary |
| Byte order | Little-endian (consistent with Windows CE / Windows Mobile platform) |
| Container | Proprietary Microsoft binary - format undocumented and not publicly reverse-engineered |
| Magic bytes | None publicly documented |
| Encryption | None documented |
| Typical size | 1 MB - 100 MB (full device backup including contacts, messages, photos, and application data) |
| Created by | ActiveSync Backup/Restore wizard (ActiveSync versions 3.x through 4.1 only) |
| Restore compatibility | ActiveSync 4.0 or 4.1 on Windows XP only - no later software reads .stg files |
| Feature removal | ActiveSync 4.2 dropped Backup/Restore entirely; .stg creation and restoration no longer possible in version 4.2 and later |
| Host platform | Windows XP; not supported on Windows Vista or later even with Windows Mobile Device Center |
| Device platform | Windows Mobile and Pocket PC devices (not Windows Phone 7/8 or later) |
| Data scope | Contacts, calendar entries, e-mail, photos, application data, and device settings |
| Format status | Stranded - effectively inaccessible without a Windows XP environment running ActiveSync 4.0 or 4.1; no official extraction tools remain available |
| Released | circa 2000, with Microsoft ActiveSync 3.x |
| Latest version | ActiveSync 4.1 (last version with backup/restore via STG; feature removed in 4.2) |
STG conversions
Community Q&A
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