EMC has overtaken HP to become the top seller of external disk-based storage, according to IDC research.

With just under $3 billion in revenue in 2004, up 18.4 percent from the year before, EMC boasts 21.1 percent of the market. HP's sales on the other hand have fallen to $2.6 billion, down 6.3 percent year-over-year, giving it an 18.7 percent share.

"This is the first time since HP acquired Compaq that EMC has come back to overtake external storage," said Brad Nisbet, a program manager with IDC. "EMC is firing on all cylinders."

IBM and Hitachi Data Systems were ranked third and fourth respectively, with sales of $1.8 billion and $1.2 billion. Dell came fifth although it is the fastest growing vendor with revenue up 18.7 percent.

Overall, sales of external disk-based storage systems were up 4.7 percent for the year, totalling $14.2 billion, but that growth slowed to less than one percent during the fourth quarter.

IBM's poor showing was caused by delays in shipping the DS6000 and DS8000 storage systems, Nisbet said. "They announced some new products on their high-end and they weren't ready," he said. "Their customers are either waiting for first-quarter availability or it stands to reason that EMC benefitted from that delay."