Cochrane library, a collection of databases containing high-quality evidence in healthcare, is produced by Cochrane collaboration.

Cochrane Library includes Cochrane Database of Systematic Reviews (CDSR), the Cochrane Central Register of Controlled Trials (CENTRAL), and Cochrane Clinical Answers.
Most heavily used databases are Database of Systematic Reviews and Central Register of Controlled Trials (CENTRAL) .

Finding Cochrane Reviews

Cochrane Systematic Reviews are produced by Cochrane Collaboration Review Group members who use explicit methodology “aimed at minimizing bias” and often viewed as the gold standard for conducting systematic reviews. This methodology is outlined in Cochrane Handbook. Researchers conducting systematic reviews outside of Cochrane collaboration can still use Cochrane methodology as a benchmark.

All current Cochrane Reviews can be found not just on the Cochrane Library itself, but via other databases as well, such as Pubmed and Embase. The biggest difference between searching within Cochrane Library compared to other databases, is that in Cochrane Library only the current or most recent review is retrieved in a search, whereas all versions can be located when searching PubMed or Embase (as seen in the example here). All Cochrane Reviews, including the superseded versions, can be found in Cochrane Library by browsing all issues of the CDSR.

Finding Central Register of Controlled Trials (CENTRAL) content

CENTRAL contains mostly RCTs (randomized controlled trials) which come from the outside sources, e.g. bibliographic databases such as Pubmed, Embase and CINAHL, unpublished sources, hand searching the literature, and web sources such as clinical trials.gov, World Health Organization.
Although trials ingested from Pubmed, Embase, CINAHL and select other sources can be found separately via those databases and websites, CENTRAL as a whole can be searched only via the Cochrane Library.

The advantage of finding controlled trials via bibliographic databases Pubmed, Embase or CINAHL separately lies in the use of the advanced functionality of those databases, all of which may not be available in the Cochrane Library original interface. Yet, since CENTRAL contains controlled trial records from other sources as well, it should be always searched by researchers conducting systematic reviews and meta-analyses, in addition to bibliographic databases.