HP Workstation x4000 hp workstation x4000 - Technical Reference manual - Windo - Page 39

System Memory and Processors System Memory System Memory The main memory for the x4000 Workstation is not located on the system board. Instead, a Memory Expander Card (MEC) plugs into the system board and contains up to eight memory modules. PC800 Rambus In-Line Memory Modules (RIMMs) with Error Correction Code (ECC) are installed on the MEC in pairs. Rambus The layout of RDRAM channels on the MEC follows Rambus recommendations that minimize trace noise. This puts pair members diagonal to each other on the MEC. RDRAM achieves high speed transmission through a combination of techniques: • dense packaging • high quality transmission lines • topology The MEC RIMMs must be loaded in a specific order. Memory loading rules are explained in "Upgrading Memory on the 8-RIMM MEC" on page 159. Each direct RDRAM channel contains two RIMM slots and is terminated at the end opposite from the memory controller. If only one RIMM is in the channel then the other slot must be filled with a Continuity RIMM (CRIMM) in order to allow a continuous path from the controller, through both slots, to the hard-wired terminator at the other end. Eight-RIMM MEC The eight-RIMM MEC can have the voltage refulator hardwaired on the MEC or it may have the removable module (VRM). The MEC shown in Figure 3-1 has a VRM slot. Chapter 3 39