Sun Microsystems has sued network-attached processing specialist Azul Systems for patent infringement - despite Azul's attempt to head it off with its own lawsuit last month.

Sun asked a California court on Wednesday to order Azul to pay damages and stop infringing Sun patents on memory technology damages. The filings, made in the San Jose division of the US District Court for the Northern District of California, counter a suit Azul filed in March, asking the court to block just such a move.

In March, Azul announced that Sun had threatened to sue it for patent infringement and abuse of trade secrets, and filed suit to prevent Sun from doing so.

Now, Sun has made good on the alleged threat, asking for a jury trial to consider its claim for exemplary and punitive damages to deter Azul from infringing its patents.

The case relates to technology for improving the performance of microprocessors through the use of "speculative locking" and transactional memory, which Azul is now using in its products. Sun claims Azul is infringing patents related to Sun's prior research in the field, and that it abused trade secrets by poaching Sun employees familiar with the technology. Sun also said the employees had signed agreements not to disclose or make use of their knowledge of Sun's intellectual property.

One of the former Sun executives named in the suit is Stephen DeWitt, the former chief executive officer (CEO) of server appliance manufacturer Cobalt Networks, which Sun bought in 2000. When DeWitt went on to become chief executive of Azul, he broke a non-compete agreement he signed when Sun bought Cobalt, sun alleges.

Sun said that by hiring DeWitt and nine other former Sun employees named in the court filing, Azul improperly accessed Sun technology, allowing Azul to bring products to market more quickly.