RAM Expansion

The main logic board has four RAM expansion slots for DDR SDRAM DIMMs. At least one of the RAM expansion slots contains a factory installed DIMM.

The DIMMs can be installed one or more at a time. The system supports linear memory organization; no performance gains are seen when two DIMMs of the same size are installed. Any supported size DIMM can be installed in any DIMM slot, and the combined memory of all of the DIMMs installed is configured as a contiguous array of memory.

The maximum memory size supported by the Xserve computer is 2 GB.

This section covers:

DIMM Specifications
RAM Addressing

DIMM Specifications

The RAM expansion slots accept 184-pin DDR333 SDRAM DIMMs that are 2.5 volt, unbuffered, 8-byte, nonparity, and PC2700 compliant (2700 Mbytes/second bus bandwidth).

Mechanical Specifications

The mechanical design of the SDRAM DIMM is defined by the JEDEC Standard MO-206. To find this specification on the World Wide Web, refer to “RAM Expansion Modules”.

The maximum height of DIMMs for use in the Xserve computer is 1.25 inches.

Electrical Specifications

The electrical design of the SDRAM DIMM is defined by the JEDEC specification JESD21-C, MODULES4_20_4, Release 11b. To find this specification on the World Wide Web, refer to “RAM Expansion Modules”.

The Serial Presence Detect (SPD) EEPROM specified in the JEDEC standard is required and must be set to properly define the DIMM configuration. The EEPROM is powered on 3.3V. Details about the required values for each byte on the SPD EEPROM can be found on pages 68–70 of the JEDEC specification.

Important

For a DIMM to be recognized by the startup software, the Serial Presence Detect feature must be programmed properly to indicate the timing modes supported by the DIMM.

RAM Addressing

Signals A[0–12] on each SDRAM DIMM make up a 13-bit multiplexed address bus that can support several different sizes of SDRAM devices. Table 4-1 shows the address multiplexing modes used with various devices.

Table 4-1 Address multiplexing modes for SDRAM devices