Technical information

CHAPTER 4
Expansion Features
70 RAM Expansion Slots
SO-DIMMS, one with a height up to 1.5 inches and the other with a height up to
2.0 inches.
IMPORTANT
The JEDEC specifications for the heights of the SO-DIMMs
gives a plus-or-minus 0.15 mm tolerance. In the PowerBook
G3 Series computer, the specified heights for the
SO-DIMMs are maximum heights. ▲
The JEDEC specification defines the maximum depth or thickness of an
SO-DIMM as 3.8 mm. That specification is also a maximum: Modules that
exceed the specified thickness can cause reliability problems.
Electrical Design of RAM SO-DIMMs 4
The electrical characteristics of the RAM SO-DIMM are given in section 4.5.6 of
the JEDEC Standard 21-C, release 7. The specification is available from the
Electronics Industry Association’s web site, at
http://www.eia.org/jedec/download/freestd/pub21/
The specification defines several attributes of the DIMM, including storage
capacity and configuration, connector pin assignments, and electrical loading.
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
the PowerBook G3 Series 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 (144 Pin SDRAM SO–DIMM,
PD INFORMATION) of the JEDEC standard 21-C specification, release 7.
Because the SO-DIMM connector has only two clock lines, and each clock line is
limited to only 4 loads, an SO-DIMM with more than 8 SDRAM devices must
have buffers on the clock lines. The buffers must be zero-delay type, such as
phase-lock loop (PLL), which regenerates the clock signals. For example, the
computer can support a 128-MB SO-DIMM using 16 devices and a PLL clock
buffer.
SDRAM Devices 4
The SDRAM devices used in the RAM expansion modules must be self-refresh
type devices for operation from a 3.3-V power supply. The speed of the SDRAM
devices must be 100 MHz or greater.