Editing Cabinet (file format) (section)

== Design ==

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 [[solid compression|single compressed block]], which provides more efficient compression than individually compressing each file.

Every entry in a folder has to be a file.<ref name="msdn.microsoft.com">[https://msdn.microsoft.com/en-us/library/bb267310.aspx Microsoft Cabinet Format]</ref> 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<ref>{{cite web|title=Microsoft Cabinet Software Development Kit|url=https://support.microsoft.com/kb/310618|work=Support|publisher=Microsoft|access-date=27 March 2013}}</ref>) as well as {{samp|lcab}}<ref>{{cite web|title=lcab|url=http://freecode.com/projects/lcab|work=Freecode|publisher=Dice|access-date=27 March 2013}}</ref> and {{samp|cabextract}}<ref>{{cite web|title=cabextract|url=https://www.cabextract.org.uk/}}</ref> (third-party [[open-source software|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.<ref>{{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}}</ref>

The CAB file format may employ the following [[compression algorithm]]s:

* [[DEFLATE]]: invented by [[Phil Katz]], the author of the [[ZIP file format]] (specifically, the MSZIP encapsulation)<ref>{{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}}</ref>
* Quantum compression: licensed from David Stafford,<ref>{{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}}</ref>{{dead|date=October 2023}} the author of the Quantum archiver (not available in all versions of makecab.exe/diamond.exe)<ref>{{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 }}</ref><ref>{{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}}</ref>
* [[LZX]]: invented by [[Jonathan Forbes (programmer)|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.