CHAPTER 4
Expansion Features
Mechanical Design of DDR RAM SO-DIMMs
The RAM expansion modules used in the PowerBook G4 17-inch computer are PC2700 DDR333 RAM SO-DIMMs, as defined in the JEDEC specifications.
The mechanical characteristics of the RAM expansion SO-DIMM are given in the JEDEC specification for the DDR SO-DIMM. The specification number is JEDEC JESD95. To obtain a copy of the specification, see the references listed at “RAM Expansion Modules” (page 61).
The specification defines SO-DIMMs with nominal heights of 1.0, 1.25, 1.5, and 2.0 inches. The PowerBook G4 17-inch computer can accommodate SO-DIMMS with heights of 1.25 inches or less.
Important: The PowerBook G4 17-inch computer can not accept a 1.5 or 2-inch SO-DIMM.
The JEDEC specification defines the maximum depth or thickness of an SO-DIMM as 3.8 mm. Modules that exceed the specified thickness can cause reliability problems.
Electrical Design of DDR RAM SO-DIMMs
SO-DIMMs for the PowerBook G4 17-inch computer are required to be PC2700 compliant. For information about the PC2700 specifications, see the references at “RAM Expansion Modules” (page 61).
The electrical characteristics of the DDR RAM SO-DIMM are given in section 4.5.6 of the JEDEC Standard 21-C, release 7 (JESD-21C). To obtain a copy of the specification, see the references listed at “RAM Expansion Modules” (page 61).
The JEDEC and Intel specifications define several attributes of the DIMM, including storage capacity and configuration, connector pin assignments, and electrical loading. The specifications support SO-DIMMs with either one or two banks of memory.
Important: The memory controller on the PowerBook G4 17-inch computer uses a separate CKE signals for each bank, as called out in the JEDEC specification. SO-DIMMs that have all the CKE pins connected together do not operate properly.
The JEDEC specification for the SO-DIMM defines a Serial Presence Detect (SPD) feature that contains the attributes of the module. SO-DIMMs for use in PowerBook computers are required to have the SPD feature. Information about the required values to be stored in the presence detect EEPROM is in section 4.1.2.5 and Figure 4.5.6–C (200-pin DDR SDRAM SO–DIMM, PD INFORMATION) of the JEDEC standard 21-C specification, release 7.
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.
Capacitance of the data lines must be kept to a minimum. Individual DRAM devices should have a pin capacitance of not more than 5 pF on each data pin.
54RAM Expansion Slots
