It may have been a potential bid by IBM that forced Oracle into agreeing to acquire Sun Microsystems as a whole, despite an Securities and Exchange Commission (SEC) filing showing that Oracle CEO Larry Ellison originally sought to acquire only Sun’s software assets.

The SEC filing notes that in addition to Oracle, there were two other anonymous companies competing to acquire Sun–IBM and, most likely, Hewlett-Packard. Some analysts and observers speculate that Oracle entered the fray to prevent IBM from gaining Sun’s Java software business.

In addition to Java, Sun’s software business includes the open source MySQL database, which has an estimated install base of 11 million users. Key virtualization technologies in Sun’s portfolio were also enticing to Oracle, as well as Sun’s Solaris server operating system.

According to published reports and SEC filings, Oracle was only initially interested in acquiring Sun’s software assets. It was only after IBM extracted itself from acquisition talks that Oracle stepped up to expand its offer to buy the whole of the company.

Officially, Oracle is paying $9.50 per share of Sun common stock, or $7.4 billion. Once Sun’s $2 billion cash reserve is factor into the equation, the sum of the acquisition is valued around $5.5 billion.

Since the Oracle acquisition announcement, several analysts and industry pundits have questioned Oracle’s ability and commitment to maintaining Sun’s hardware business, which includes substantial holdings in Unix servers, NAS storage and, in particular, the SPARC processors. Ellison has stood steadfast, stating that Oracle would maintain and, potentially, expand Sun’s hardware assets.