DB2 Express is priced at US$4,874 per CPU or $625 per server, plus $124 per named user.

The free database market is getting crowded. MySQL is a popular open-source relational database management system, and last year, Computer Associates International Inc. sold its open-source Ingres software to a new organization, Ingres Corp., which is aiming at the enterprise market.

Among the Big Three database makers, IBM is the last to release a free version. Microsoft was first out of the gate with SQL Server 2005 Express, which is limited to single-CPU Windows machines with 1GB of memory and 4GB of user data.

Oracle followed late last year with Database 10g Express Edition, which has been downloaded more than 100,000 times, a spokesperson said. Oracle's free software is capped at 4GB of user data, 1GB of memory and one CPU. Oracle officials declined to comment on whether the company would relax those restrictions.

Microsoft SQL Server Product Manager Carol Dullmeyer also declined to say whether Microsoft would allow its free version of SQL Server 2005 to support an unlimited number of users or database size, as IBM's free DB2 does. She said the number of users downloading SQL Server 2005 Express in the past three months has "exceeded our growth expectations by hundreds of thousands," but she declined to give a figure.