DIMM Population Rules

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This section provides the rules for adding and replacing DIMMs on a CMOD. It updates and enhances the information in DIMM Population Rules in Sun Fire X4800 Server Service Manual.

For additional information, including how to prepare the system for servicing, how to remove a CMOD, and how to remove or replace DIMMs, see Removing and Installing Components in Sun Fire X4800 Server Service Manual.

Each CMOD has 32 DIMM slots, with 16 allocated to each CPU. CMODs are shipped with configurations of 16 or 32 DIMMs, meaning that each CPU has either 8 or 16 DIMMs.

On a CMOD with 16 DIMMs, you can replace DIMMs, and you can add additional DIMMs.
On a CMOD with 32 DIMMs, you can replace DIMMs, but because they are fully populated, you cannot add DIMMs.

The rules for adding and replacing DIMMs are:

When you replace DIMMs, you must match parameters.
When you add DIMMs, you must match parameters and populate them in the specified order.

Matching Parameters

There are four parameters to consider when replacing DIMMs: size, speed, density, and manufacturer's model number.

All of the DIMMs in the CMOD must be the same size, speed, and density.
Both of the DIMMs in a pair must be the same size, speed, and density, and have the same manufacturer's model number. The pairs are 0/4, 1/5, 2/6, 3/7, 8/12, 9/13, 10/14, and 11/15.

The following table shows the requirements.

Parameter and Value	Match Within CMOD	Match Within Pairs
Size — 2 GB, 4 GB, or 8 GB	x	x
Speed — 1066 MHz JEDEC or DDR3 ECC RDIMMs	x	x
Density — Single or dual rank	x	x
Manufacturer's model number		x

DIMM Population Order

You can add DIMMs according to the following rules:

You cannot add DIMMs to a 32–DIMM system because it is already fully populated.
All DIMMs must have their parameters matched, as described above.
Only four or eight DIMM upgrades are supported. As a result, all color blocks must be either full or empty.

DIMMs must be populated in the correct order.

On a 16–DIMM CMOD, all the blue and white slots should already be populated.

When you add DIMMs, fill the black slots (D1/D5 and D10/14) first, and fill the green slots (D3/D7 and D11/D15) last.

Order	Numbers	Slot Color	Minimum Configuration
1	D0/D4	Blue	Filled by default
2	D8/D12	Blue	Filled by default
3	D2/D6	White	Filled by default
4	D10/D14	White	Filled by default
5	D1/D5	Black	Fill these first
6	D9/D13	Black	Fill these first
7	D3/D7	Green	Fill these last
8	D11/D15	Green	Fill these last

The following figure shows the location of the DIMMs on the CMOD.

Legend	Description
1	CPU 0
2	CPU 1
3	Towards the front of the CMOD