cabinet (file format)

A CAB archive can contain up to 65,535 folders (distinct from standard operating system directories), each of which can contain up to 65,535 files for a maximum of 4,294,836,225. Internally, each folder is treated as a single compressed block, which provides more efficient compression than individually compressing each file.

Every entry in a folder has to be a file.[https://msdn.microsoft.com/en-us/library/bb267310.aspx Microsoft Cabinet Format] 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 folders and files:

{{tree list}}

• CAB file
• First folder
• {{samp|Records/Student_01.tsv}}
• {{samp|Records/Photos/Student_01.jpg}}
• Second folder
• {{samp|Records/Student_02.tsv}}
• {{samp|Records/Photos/Student_02.jpg}}

{{tree list/end}}

How paths should be handled is not specified in the CAB file format, leaving it to the software implementation:

• Some affix file paths to filenames only, as if all files in a CAB archive are in a single folder. IExpress works this way, as does Microsoft Windows Explorer, which can open CAB archives as a folder.
• Some can store the paths, and upon extraction, create folders as necessary. {{mono|CABARC.EXE}} and {{mono|EXTRACT.EXE}} (tools from Microsoft Cabinet SDK{{cite web|title=Microsoft Cabinet Software Development Kit|url=https://support.microsoft.com/kb/310618|work=Support|publisher=Microsoft|access-date=27 March 2013}}) as well as {{samp|lcab}}{{cite web|title=lcab|url=http://freecode.com/projects/lcab|work=Freecode|publisher=Dice|access-date=27 March 2013}} and {{samp|cabextract}}{{cite web|title=cabextract|url=https://www.cabextract.org.uk/}} (third-party open-source tools) work this way.
• {{mono|EXPAND.EXE}}, only since version 6 (which is included from Windows Vista to above) can extract files to their paths. The previous versions don't do it.{{cite web|url=http://ss64.org/viewtopic.php?id=1816|title=[Undocumented] [Bugs] Expand.exe (more about it) (Page 1) / Windows CMD Shell / SS64 Forum|website=ss64.org|access-date=21 April 2018}}

The CAB file format may employ the following compression algorithms:

• DEFLATE: invented by Phil Katz, the author of the ZIP file format (specifically, the MSZIP encapsulation){{cite web |title=[MS-MCI]: Microsoft ZIP (MSZIP) Compression and Decompression Data Structure |url=https://docs.microsoft.com/en-us/openspecs/exchange_server_protocols/ms-mci/ |website=docs.microsoft.com |date=13 October 2020 |language=en-us}}
• Quantum compression: licensed from David Stafford,{{Cite book|last=Salomon|first=D. (David)|url=https://archive.org/details/datacompressionc00salo_251/page/n206/mode/2up|title=Data compression : the complete reference|date=2007|publisher=London : Springer|others=Library Genesis|isbn=978-1-84628-602-5|pages=187}}{{dead|date=October 2023}} the author of the Quantum archiver (not available in all versions of makecab.exe/diamond.exe){{cite web |title=Quantum compression format |url=http://www.russotto.net/quantumcomp.html |website=Matthew Russotto |access-date=29 March 2022 |archive-date=11 May 2021 |archive-url=https://web.archive.org/web/20210511035452/http://www.russotto.net/quantumcomp.html |url-status=dead }}{{Cite web |date=2011-03-04 |title=Cabinet File Format – Open Specifications Documentation |url=https://download.microsoft.com/download/4/d/a/4da14f27-b4ef-4170-a6e6-5b1ef85b1baa/[ms-cab].pdf#page=9 |url-status=live |archive-url=https://web.archive.org/web/20161118224049/https://download.microsoft.com/download/4/d/a/4da14f27-b4ef-4170-a6e6-5b1ef85b1baa/[ms-cab].pdf |archive-date=2016-11-18 |archive-format=PDF |access-date=2023-02-15 |publisher=Microsoft Corporation}}
• LZX: invented by Jonathan Forbes and Tomi Poutanen, given to Microsoft when Forbes joined the company
• NULL: stored

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.

{{Main|Comparison of file archivers}}

Microsoft Windows supports creating CAB archive files using the makecab command-line utility. It supports extracting the contents of a CAB archive files using File Explorer, Setup API, and using the command-line commands expand.exe,[https://ss64.com/nt/expand.html expand – Windows CMD – SS64.com] extract.exe and extrac32.exe.[https://www.thewindowsclub.com/extract-cab-file-using-command-line How to extract CAB File using command line tools in Windows 10][https://ss64.com/nt/extract.html Extrac32 – Uncompress files – Windows CMD – SS64.com]

Other well-known software with CAB archive support includes WinZip, WinRAR or 7-Zip. The aforementioned cabextract is a common tool for Linux systems,[https://www.systranbox.com/how-to-extract-cab-files-in-linux/ How to extract CAB files in Linux]{{Dead link|date=August 2023 |bot=InternetArchiveBot |fix-attempted=yes }} but is only capable of extracting archives. The gcab tool however can both extract and create CAB archives.[https://gitlab.gnome.org/GNOME/gcab gcab project on GNOME] For a full list, see {{section link|Comparison of file archivers|archive formats}}.

A variety of Microsoft installation technologies use the CAB format: these include Windows Installer, Windows Setup (from Windows 95 to Windows Server 2003), Setup API, Device Installer, Theme Pack 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 usually include one or more embedded CAB files.

Windows uses the cabinet format to archive its Component-Based Servicing (CBS) log, which is kept in the folder {{mono|C:\Windows\Logs\CBS}}. A bug in the compression process can cause run-away generation of useless log files both in that folder and in {{mono|C:\Windows\Temp}}, which can consume disk storage until completely filling the hard drive.{{Cite web|url=https://social.technet.microsoft.com/wiki/contents/articles/38259.clean-up-component-based-servicing-logs.aspx|title=Clean Up Component-Based Servicing logs|date=7 July 2017|website=Microsoft TechNet}}{{Cite web|url=https://www.computerworld.com/article/3112358/microsoft-windows/windows-7-log-file-compression-bug-can-fill-up-your-hard-drive.html|title=Windows 7 log file compression bug can fill up your hard drive|last=Leonhard|first=Woody|date=2016-08-25|website=Computerworld|language=en|access-date=2019-01-08|archive-date=8 January 2019|archive-url=https://web.archive.org/web/20190108145549/https://www.computerworld.com/article/3112358/microsoft-windows/windows-7-log-file-compression-bug-can-fill-up-your-hard-drive.html|url-status=dead}} Deletion of the files without following a specific procedure can cause the deleted files to be regenerated at an increased pace.

On Linux systems, CAB archives are used by fwupd to distribute firmware updates from hardware vendors{{cite web |title=LVFS: Hardware Vendors |url=https://fwupd.org/lvfs/docs/vendors |website=Linux Vendor Firmware Service Project |access-date=3 May 2022}} that can be flashed on non-volatile memory.

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.{{cite web|url=https://github.com/twogood/unshield|title=twogood/unshield|website=GitHub|access-date=21 April 2018}} This format has a different magic number of {{tt|ISC(}}.{{cite web |title=kyz/libmspack: doc/magic |url=https://github.com/kyz/libmspack/blob/master/cabextract/doc/magic |website=GitHub |date=2 January 2022 |language=en}}

Windows CE software is distributed as CAB files where the first file inside, ending with extension ".000", details how it is installed.{{cite web |title=Windows CE installation cabinet (.CAB) file format |url=https://www.cabextract.org.uk/wince_cab_format/ |website=cabextract}}

Microsoft Installer .msi files sometimes contain CAB files, but are themselves in the Compound File Binary Format which has to be decoded first. Software like lessmsi can be used to unpack these files.

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.

• List of archive formats

{{reflist}}

{{Wikibooks|Guide to Windows Commands}}

• [https://msdn.microsoft.com/en-us/library/ms974336.aspx Microsoft Cabinet SDK] – updated versions of these resources are available in the Microsoft Windows SDK
• [http://www.mdgx.com/add.htm#CAB Cabinet Software Development Kit (CAB SDK)] – downloads of all Microsoft CAB SDK versions (free)

{{Archive formats}}

{{Windows commands}}

Category:Archive formats

Category:Windows administration