NEW YORK (CNN/Money) - Sun Microsystems Inc. is buying Storage Technology Corp. in a $4.1 billion cash deal, the companies announced Thursday.

The deal, if completed, will pay StorageTek (Research) shareholders $37 a share, or an 18.5 percent premium on Wednesday's close.

The deal is expected to close in the late summer or early fall.

StorageTek makes computer hardware and software that helps business and government customers back-up and manage large amounts of computer data. Sun (Research) is the leading maker of UNIX-based servers used to power computer networks and Web sites, but it also provides storage and backup products.

The deal is expected to add to Sun's earnings per share, excluding special items, within 12 months of closing, according to the statement from the two companies.

Shares of Sun gained 18 cents, or about 5 percent, to $4.08 in pre-market trading on Inet following the announcement, while shares of StorageTek gained $5.62 to $36.85 in pre-market trading, close to the offer price.