Filename extension .cab Magic number MSCF | Uniform Type Identifier (UTI) public.archive.cab Developed by Microsoft | |
Internet media type application/vnd.ms-cab-compressed UTI conformation public.datapublic.archive | ||
Cabinet (or CAB) is an archive file format for Microsoft Windows that supports lossless data compression and embedded digital certificates used for maintaining archive integrity. Cabinet files have .cab filename extensions and are recognized by their first 4 bytes MSCF. Cabinet files were known originally as Diamond files.
Contents
The CAB file format may employ the following compression algorithms:
A CAB archive can reserve empty spaces in the archive as well as for each file in the archive, for some application-specific uses like digital signatures or arbitrary data. CAB format is used by a variety of Microsoft installation technologies including Windows Installer, Setup API, Device Installer and AdvPack (used by Internet Explorer to install ActiveX components). CAB files are also often associated with self-extracting programs like IExpress where the executable program extracts the associated CAB file. CAB files are also sometimes embedded into other files. For example, MSI and MSU files (the latter are CAB files with just another filename extension) usually included one or more embedded CAB files.
File structure
A CAB archive can contain up to 65535 CAB-folders, (not to be confused with file system folders) each can contain up to 65535 files. Internally, each CAB-folder is treated as a single compressed block, which provides more efficient compression than individually compressing each file.
Every entry in a CAB-folder has to be a file. Due to this structure, it is not possible to store empty folders in CAB archives.
The following shows an example a CAB file structure, demonstrating the relationship between CAB-folders and files:
How paths should be handled is not specified in the CAB file format, leaving it to the software implementation.
lcab and cabextract (third-party open-source tools) work this way.Software
Software that can extract the contents of a CAB archive file are numerous, including Microsoft Windows itself (through File Explorer, Setup API, expand.exe or extract.exe) as well as well-known software such as WinZip, WinRAR or 7-Zip. However, fewer programs can create CAB archives. For a full list, see Comparison of file archivers § archive formats.
The Windows program makecab.exe is used to create CAB archives:
.ddf filename extension) and create a CAB archive containing multiple files in a flat or hierarchical structure like a file system.Related formats
The .cab filename extension is also used by other installer programs (e.g. InstallShield) for their own proprietary archiving formats. InstallShield uses zlib for compression (see Deflate), but their headers are not the same as for Microsoft CAB files so they are incompatible and cannot be manipulated or edited with the programs that are made for standard Cabinet format. Specialized third-party utilities, such as Unshield, can extract this specific proprietary format.
Microsoft Publisher has a "Pack and Go" feature that bundles a publisher document, together with all external links, into a CAB file with a .PUZ extension. These files are meant to be activated with a companion .EXE file which is distributed along with the .PUZ file. These files may be opened with any CAB file extraction program.