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| operating_system = {{plainlist|
* [[IBM AIX|AIX]], [[HP-UX]], [[Linux]], [[macOS]], [[Solaris (operating system)|Solaris]], [[Microsoft Windows|Windows]]<ref name="platforms">{{cite web|url=https://www-01.ibm.com/common/ssi/cgi-bin/ssialias?infotype=an&subtype=ca&appname=gpateam&supplier=877&letternum=ENUSZP16-0128|title=IBM Rational ClearCase and IBM Rational ClearQuest V9.0 deliver enterprise collaborative change and configuration management solution enhancements for software and systems development teams|date=March 15, 2016|publisher=[[IBM]]}}</ref>
* [[z/OS]] (limited client)<ref>{{cite web|url=https://www.ibm.com/docs/en/rational-clearcase/109.0.2?topic=installing-using-zos-extensions
|title=Installing and using z/OS Extensions}}</ref>
}}
== History ==
ClearCase was developed by [[Atria Software]] and first released in 1992<ref>{{cite web | url = httphttps://web.archive.org/web/20090802071539/https://www.findarticles.com/p/articles/mi_m0SMG/is_n13_v12/ai_12606942 | title = ClearCase - Atria Software Inc.'s software configuration management system - New Products: Development Tools - Brief Article - Product Announcement | publisher = Software Magazine | date = September 15, 1992 | access-date = 2007-12-01 }}</ref> on Unix and later on [[Windows]]. Some of the Atria developers had worked on an earlier, similar system: ''DSEE'' ([[Apollo Domain|Domain]] Software Engineering Environment) from [[Apollo Computer]]. After [[Hewlett-Packard]] bought [[Apollo Computer]] in 1989, those developers left to form Atria.<ref>{{cite web | url = http://www.cmcrossroads.com/cgi-bin/cmwiki/view/CM/HistoryOfCM | title = Key dates in Hardware/Software Configuration Management History | publisher = CM Crossroads LLC | year = 2007 }}</ref><ref>{{cite web | url = httphttps://web.archive.org/web/20090802063953/https://www.findarticles.com/p/articles/mi_m0SMG/is_n8_v15/ai_17338017 | title = Complex development earns Atria an IS role; hot Unix vendor's move to Windows and NT opens IS doors - Company Profile | author = Michael Bucken | date = August 1995 | publisher = Software Magazine }}</ref><ref>{{cite newsgroup | url = http://lists.gnu.org/archive/html/info-cvs/2004-12/msg00237.html | title = Re: cvs vs. clearcase? | author = Andrew DeFaria | date = December 21, 2004 }}</ref> Atria later merged with [[Pure Software]] to form PureAtria.<ref>{{cite web | url = https://query.nytimes.com/gst/fullpage.html?res=940CE6DE1639F934A35755C0A960958260 | title = Pure Software To Buy Astria In Stock Deal<!-- original article misspells Atria in title --> | author = Lawrence M. Fisher | date = June 7, 1996 | work = The New York Times | access-date = 2007-12-01 }}</ref> That firm was acquired by [[Rational Software]], which was purchased by [[IBM]] in 2003.<ref>{{ cite web | url = http://www-03.ibm.com/press/us/en/pressrelease/243.wss | title = IBM Reports 2003 First-Quarter Results | date = April 14, 2003 | publisher = IBM | access-date = 2008-01-09 }}</ref> IBM continues to develop and market ClearCase. In September 2016, IBM announced a strategic partnership with HCL Technologies that will allow for accelerated development.
DSEE introduced many concepts that were adopted by ClearCase. The Apollo Domain file system allowed special handler programs to intervene during file access. DSEE made use of this feature to invisibly substitute a versioned copy when a particular file was opened.<ref>{{cite web |url = httphttps://web.archive.org/web/20070224072638/https://www.findarticles.com/p/articles/mi_m0HPJ/is_n3_v42/ai_10916486/ |title = DSEE: a software configuration management tool |author = David c. Lubkin |date = June 1991 |publisher = Hewlett-Packard Journal |access-date = July 17, 2010 }}</ref> With the versioning specification resident in the user environment, all accesses to versioned files were redirected, including such mundane accesses as printing, viewing in a generic text editor etc.
DSEE relied heavily on a file that described all the software modules and their dependencies. The file had to be generated manually, which was a major impediment to its use in large systems. However, once generated, it enabled DSEE to calculate the optimum way to perform a build, re-using all modules that had previously been processed and whose version specifications matched the specifications for the build.
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* {{cite web | url = httphttps://techpubs.sgiirix7.com/library/dynaweb_docs/0620/SGI_EndUser/books/ClrC_UG/sgi_htmltechpubs/index007-2369-001.htmlpdf | title = CASEVision/ClearCase User's Guide, Document Number: 007-2369-001 | first = John | last = Posner | year = 1994 | publisher = Silicon Graphics, Inc. | url-status = dead | archive-url = https://web.archive.org/web/20071102161629/http://techpubs.sgi.com/library/dynaweb_docs/0620/SGI_EndUser/books/ClrC_UG/sgi_html/index.html | archive-date = 2007-11-02 }}
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