On 5/18/18 11:00 AM, Alan Perry via cctalk wrote: > On the back, the bottom, wider slot was open, the two slots above occupied, and the upper two had blanking plates. the empty slot is where the CPU goes. the upper two are 'DIO' slots more than you ever wanted to know is at http://bitsavers.org/pdf/hp/9000_300 the most common 300 series that show up are the 310/320