Sun Microsystems has upgraded its lower-end Sun Fire 280R servers with a newer 900MHz CPU (central processing unit). The 280R was the first server to ship with Sun's new UltraSparc III chip, but it used 750MHz chips when it went on sale a year ago. The new model means a performance improvement of about 20 percent, Palo Alto, Calif.-based Sun said. Customers can upgrade existing servers by swapping out the CPU and cooling fans. A new two-processor 280R costs $22,995 with 2GB of memory and two 36GB hard disks.