Sun Microsystems, Inc.

Processor VRM

Each processor receives core voltage input from an individual voltage regulator module (VRM). The VRMs
regulate the system current and voltage according to the VID code output by the CPU package. The VRM is a
DC-to-DC point-of-load convertor specified for +12 Volt input and programmable 100 Amp output. The VRM is
different on the new 8-DIMM Processor Boards to accommodate the additional memory requirements.
Memory Architecture
Each CPU includes a low-latency, high-bandwidth, integrated memory controller that reduces latencies during
memory access over traditional Intel front-side bus-based memory controllers, and each supports up to four
ECC Registered DDR400 (Sun Fire X4600) or up to eight ECC Registered DDR2/667 (Sun Fire X4600 M2)
memory modules. Although the AMD Opteron processor's memory controller works in 64-bit or 128-bit mode
ECC operation, for best performance results, it is recommended to run 128-bit ECC operation mode. To run in
128-bit mode, DIMMs should be populated in pairs such that they occupy one-half of the AMD Opteron
processor's 128-bit controller interface. The controller supports 1 bit per byte ECC and supports DDR400
(PC3200) registered DDR SDRAM modules. The Sun Fire X4600 uses DDR400 (PC3200) registered DDR
SDRAM modules and the Sun Fire X4600 M2 uses DDR2/667 (PC2-5300) registered DDR SDRAM modules
The Sun Fire X4600 server has 4 DDR DIMM slots per CPU that are color-coded white and black to indicate
population order (white = 0,1 and black = 2,3; white pair first). LED fault indicators controlled by the ILOM
Service Processor provide the ability to easily identify failed DIMM modules. Memory capacity scales with the
number of processors, so memory attached to an unpopulated processor slot is unaddressable. As a result, an
dual-socket machine can support a maximum of eight DIMMs. A fully populated, eight-CPU server supports a
maximum of 32 DIMMS or 128 GB of memory.
Figure 2-6: Logical View of Sun Fire X4600 8-DIMM Memory
The Sun Fire X4600 M2 server has a new processor board that supports 8 DDR DIMM slots per CPU that are
color-coded white and black to indicate population order (black = 0,1, 2, 3 and white = 4, 5, 6, 7). Memory is
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