From Apple Dev Notes
RAM Expansion
The main logic board of some configurations of the Power Mac G5 computer have four pairs of DDR SDRAM expansion slots for unbuffered DDR400 (PC3200) dual in-line memory modules (DIMMs) for a maximum memory of 8 GB. The main logic board of other configurations of the Power Mac G5 computer have 2 pairs of DDR SDRAM expansion slots for unbuffered DDR333 (PC2700) dual in-line memory modules (DIMMs) for a maximum memory of 4 GB.
Each DIMM can contain 256 and 512 MB (also is capable of 128 MB, 1 GB, and has future expansion ability of 2 GB) of double data rate synchronous dynamic RAM (DDR SDRAM). At least one pair of the RAM expansion slots contains factory installed DIMMs.
Additional DIMMs must be installed in pairs of the same size. The slot pairs are numbered: J11 and J12, J13 and J14, J41 and J42, and J43 and J44; see Figure 4-1 for slot locations and numbering for both the 8-slot and 4-slot configurations. When installing additional memory, populate starting with the lowest slot pair numbers. The combined memory of all of the DIMMs installed is configured as a contiguous array of memory.
For all microprocessor speeds and for both DDR400 (PC3200) and DDR333 (PC2700) SDRAM DIMMs, the Power Mac G5 supports CAS latencies of 2, 2.5, 3, 4, and 5.
And the Power Mac G5 RAM requirement
DIMM Specifications
The RAM expansion slots accept 184-pin DDR SDRAM DIMMs that are 2.5 volt, unbuffered, 8-byte, nonparity, and DDR400-compliant (PC3200) or DR333-compliant (PC2700).
Important
DDR266 (PC2100) or slower DIMMs do not work in the Power Mac G5 computer.
Important
DIMMs with any of the following features are not supported in the Power Mac G5 computer: registers or buffers, PLLs, ECC, parity, or EDO RAM.
Mechanical Specifications
The mechanical design of the DDR 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" (page 80).
The maximum height of DIMMs for use in the Power Mac G5 computer is 2 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" (page 80).
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 3.3 V. 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 SPD feature must be programmed properly to indicate the timing modes supported by the DIMM.
RAM Expansion
The main logic board of some configurations of the Power Mac G5 computer have four pairs of DDR SDRAM expansion slots for unbuffered DDR400 (PC3200) dual in-line memory modules (DIMMs) for a maximum memory of 8 GB. The main logic board of other configurations of the Power Mac G5 computer have 2 pairs of DDR SDRAM expansion slots for unbuffered DDR333 (PC2700) dual in-line memory modules (DIMMs) for a maximum memory of 4 GB.
Each DIMM can contain 256 and 512 MB (also is capable of 128 MB, 1 GB, and has future expansion ability of 2 GB) of double data rate synchronous dynamic RAM (DDR SDRAM). At least one pair of the RAM expansion slots contains factory installed DIMMs.
Additional DIMMs must be installed in pairs of the same size. The slot pairs are numbered: J11 and J12, J13 and J14, J41 and J42, and J43 and J44; see Figure 4-1 for slot locations and numbering for both the 8-slot and 4-slot configurations. When installing additional memory, populate starting with the lowest slot pair numbers. The combined memory of all of the DIMMs installed is configured as a contiguous array of memory.
For all microprocessor speeds and for both DDR400 (PC3200) and DDR333 (PC2700) SDRAM DIMMs, the Power Mac G5 supports CAS latencies of 2, 2.5, 3, 4, and 5.
And the Power Mac G5 RAM requirement
DIMM Specifications
The RAM expansion slots accept 184-pin DDR SDRAM DIMMs that are 2.5 volt, unbuffered, 8-byte, nonparity, and DDR400-compliant (PC3200) or DR333-compliant (PC2700).
Important
DDR266 (PC2100) or slower DIMMs do not work in the Power Mac G5 computer.
Important
DIMMs with any of the following features are not supported in the Power Mac G5 computer: registers or buffers, PLLs, ECC, parity, or EDO RAM.
Mechanical Specifications
The mechanical design of the DDR 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" (page 80).
The maximum height of DIMMs for use in the Power Mac G5 computer is 2 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" (page 80).
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 3.3 V. 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 SPD feature must be programmed properly to indicate the timing modes supported by the DIMM.
