What is the BCK file format?
.bck files store backup copies generated on the OpenVMS operating system. Backup copies are created by issuing the BACKUP command from the command line on an OpenVMS host.
OpenVMS was originally developed by Digital Equipment Corporation (DEC), later stewarded by HP/HPE, and is now developed by VMS Software Inc. (VSI). It is the successor to the original VAX/VMS series and is a system dedicated to servers and computer networks. OpenVMS offers high availability via clustering and a distributed installation system spanning multiple physical machines. The integrated backup solution based on .bck further reinforces its operational stability and data integrity.
A .bck saveset is a binary, block-structured sequential archive with a default block size of 32,256 bytes (tunable with the /BLOCK_SIZE qualifier). Each saveset preserves file contents alongside VMS-specific attributes - record format, access control lists (ACLs), and version numbers - making it distinct from generic backup containers like .bak files. Restoration requires the BACKUP utility on an active OpenVMS system, as no cross-platform reader exists for the format.
Savesets support optional compression and optional encryption (/ENCRYPT), using AES on modern OpenVMS releases or DES on older systems. Per-block CRC checksums enable the BACKUP /VERIFY command to validate a written saveset against the source. Savesets may also carry the .sav extension as an alternative to the default .bck.
Security & safety
RISK: LOWA BACKUP saveset is passive data and runs no code, so risk is low. Practical risks are operational: restoring requires a compatible OpenVMS environment, and an encrypted saveset (/ENCRYPT) cannot be restored without its key. Verify integrity with BACKUP /VERIFY. A generic .bck of unknown origin should be scanned like any downloaded file before opening with its source program.
Format details
in a nutshell- Backup Express Pro backup file - Backup created by Xpert-Design Software's Backup Express Pro on Windows (the DB's original db_name).
- Generic application backup - Various programs write a .bck as a plain renamed backup copy, similar to .bak.
Programs that open BCK files
Windows2 apps
OpenVMS BACKUP (on an OpenVMS host)
Paid Restore on OpenVMS: BACKUP saveset.bck/SAVE_SET target:[dir...] - Windows itself cannot read a saveset.
SIMH VAX/Alpha emulator (to run OpenVMS)
Open-source Run OpenVMS under SIMH on Windows, copy the saveset in, then use BACKUP to restore it. 
Linux1 app
SIMH VAX/Alpha emulator (to run OpenVMS)
Open-source Emulate a VAX/Alpha, boot OpenVMS, and restore the saveset with the BACKUP utility. Technical details
deep spec| Format type | Sequential binary saveset (block-structured) |
| Default block size | 32,256 bytes; adjustable via the /BLOCK_SIZE qualifier |
| Byte order | Little-endian (VAX, Alpha, x86-64 native) |
| Encoding | Binary |
| Compression | None by default; optional compression available with /COMPRESS |
| Encryption | Optional via /ENCRYPT qualifier - AES-256 on modern OpenVMS, DES on historical releases |
| Integrity verification | Per-block CRC; saveset can be validated against source using BACKUP /VERIFY |
| Preserved file attributes | VMS record format, ACLs, version numbers, and creation/modification timestamps |
| Associated operating system | OpenVMS (VAX, Alpha, Itanium, x86-64 architectures) |
| Restore tool | OpenVMS BACKUP utility; no native cross-platform restore tool exists |
| MIME type | application/octet-stream |
| Magic bytes | No fixed cross-platform signature; identified by internal block structure and saveset summary record |
| Typical size | A few MB to many GB, depending on saveset scope |
| Alternative extension | .sav (also conventional for OpenVMS BACKUP savesets) |
| Developer lineage | Digital Equipment Corporation (DEC) → HP/HPE → VMS Software Inc. (VSI) |
| Released | 1977 (VAX/VMS); BACKUP utility a core part of VMS from early releases |
| Latest version | OpenVMS x86-64 (VSI, 2020s) still uses the BACKUP utility |
| Specification | docs.vmssoftware.com |
BCK conversions
Community Q&A
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