Sales of data storage hardware surged in the fourth quarter, research firm IDC announced Thursday, capping a year of double-digit growth.

Total disk storage system sales climbed 13.1 percent in the quarter over the same period in 2004, said IDC, while revenues reached $6.8 billion worldwide. External disks grew even faster, showing a 17.9 percent boost over 2004's fourth quarter, and posting sales of $4.7 billion.

"The external disk storage systems market growth continued to accelerate through the year," said Brad Nisbet, program IDC manager, in a statement. "Data growth was one driver, but the availability of affordable systems that support multiple tiers of storage to address data protection, business continuity requirements, and online, active archives also contributed."

EMC held down the top spot in external disk system sales, said Nisbet, and accounted for 20.6 percent of all sales. HP was close behind at 18 percent, with IBM at 15.9 percent and Dell a distant fourth at 9.2 percent.

In total disk systems -- external and internal -- HP took top honors with a 23.1 share. IBM held down second with 20.3 percent, and EMC had third, with 14.2 percent. Global storage revenue in 2005 was up 10.7 percent over 2004, for a final tally of $23.7 billion.

Among the major vendors, Dell and IBM showed the most impressive gains over 2004. Dell grew its sales by 36.5 percent, and IBM boosted its sales by 23.8 percent.

"The sweet spot in the market during 2005 was systems priced between $50,000 and $149,999," said Natalya Yezhkova, IDC senior research analyst, in another statement. "This segment, which serves the needs of a broad range of data centers and applications, grew to over $1 billion in the fourth quarter."

Total disk storage capacity grew even faster than sales, a reflection of the continuing trend toward lower prices and larger storage systems. According to IDC, the global storage capacity in the fourth quarter was 653 petabytes, an increase of 54.6 percent over the same quarter in 2004.