Specifications

Important: DDR333 (PC2700) 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 66).

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 66).

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.

DIMM Configurations

The largest DIMM supported is a two-bank DIMM of 1 GB using 512 Mbit DDR SDRAM devices. The maximum

number of devices per DIMM is 16.

Important: Power is delivered to the Power Mac G5 during sleep mode, so do not remove DIMMs while

in sleep mode. A red light adjacent to the DIMM is illuminated when the duct door is removed and power

is present.

Table 4-1 (page 61) shows information about the different sizes of DDR SDRAM devices used in the memory

modules. The memory controller supports 64 Mbit, 128 Mbit, 256 Mbit, and 512 Mbit DDR SDRAM devices. The

device configurations include three specifications: address range, word size, and number of banks. For example,

a 1 M by 16 by 4 device addresses 1 M, stores 16 bits at a time, and has 4 banks.

Expansion

RAM Expansion