System Memory; Rambus; Eight-Rimm Mec - HP x4000 Technical Reference Manual

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.
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