From “ECO at a Glance”, Mark Weeks on About.com “The acronym ECO (Encyclopedia of Chess Openings) refers to two different but related concepts:- * A five volume reference (A-E) published by Chess Informant; and Each volume of the Encyclopedia covers 100 codes, e.g. Volume A covers A00-A99.” Chess Informant has a CD set available for purchase covering the ECO five volume reference manual, which comes in 4 different formats (CIE, PGN, CBH, CA), and has an easy searchable/retrieve capability to easily locate a specific line of play. The webaddress is: http://www.sahovski.com/products/eco/latest.php?id=346 (opens in a new browser window/tab, close that or use your browser’s back arrow/command to return here). PGN game collection files for the codes in each ECO group for studying offline may be obtained from the webaddresses listed on each of the individual ECO group pages. These ECO game collection pages are from the Bookup website; however, Bookup was replaced with a new Chess Openings Software in 2007. The link for Chess Openings Software on the pages (links below) is to the old Bookup software, so you should not use that link. I am not sure how long these webpages and files will be available. Also, the pgn files contain more variations especially for ECO A00 Irregular Openings than listed herein. There are many resources on the Internet for searching, reviewing and obtaining learning materials for openings covered by ECO. One of the largest searchable data bases on line is ChessGames.com Online Chess Games Database at www.chessgames.com/index.html – extensive search capabilities and very easy to use; can search by ECO, player, year, etc. (opens in a new browser window/tab, close that or use your browser’s back arrow/command to return here).
* A system of chess opening classification using codes A00-E99.