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Indexed file
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<p>An indexed file is a <a href="/facts/Computer_file/FjFH3Ufm">computer file</a> with an <a href="/facts/Lookup_table/ULPEAGTJ">index</a> that allows easy <a href="/facts/Random_access/1cxrCk3r">random access</a> to any <a href="/facts/Storage_record/pIYgY1Fu">record</a> given its file <a href="/facts/Unique_key/NKGBxUHR">key</a>. </p><p>The key must be such that it uniquely identifies a record. If more than one index is present the other ones are called <i>alternate indexes</i>. The indexes are created with the file and maintained by the system. </p><p><a href="/facts/IBM/QszA7nwd">IBM</a> supports indexed files with the <i>Indexed Sequential Access Method</i> (<a href="/facts/ISAM/J1Q7sty3">ISAM</a>) on <a href="/facts/OS/360_and_successors/nQbdNbx6">OS/360 and successors</a>. IBM <a href="/facts/OS/VS/cs79sdaL">virtual storage operating systems</a> added <a href="/facts/VSAM/EM2uDhjw">VSAM</a>, which supports indexed files as <a href="/facts/Key_Sequenced_Data_Set/tbCEQVAK">Key Sequenced Data Sets</a> (KSDS), with more options. Support for indexed files is built into <a href="/facts/COBOL/wVnhqs0k">COBOL</a> and <a href="/facts/PL/I/469mVYgd">PL/I</a>. Other languages with more limited I/O facilities such as <a href="/facts/C_(programming_language)/Ky2No763">C</a> support indexed files through add-on packages in a runtime library such as C-ISAM. Some of <a href="/facts/Digital_Equipment_Corporation/ztxs6keA">Digital</a>'s operating systems, such as <a href="/facts/OpenVMS/rAnHAgpD">OpenVMS</a>, support indexed file I/O using the <a href="/facts/Record_Management_Services/a5TTHAcB">Record Management Services</a>. </p><p>In recent systems, <a href="/facts/Relational_database/pEKGmJLy">relational databases</a> are often used in place of indexed files. </p>