Mechanical design of ram so-dimms, Electrical design of ram so-dimms – Apple iMac User Manual
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C H A P T E R 4
RAM Expansion
Main RAM Expansion
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Total RAM capacity using devices currently available is 128 MB and is limited
by the space available for the SO-DIMMs. The bottom slot can accommodate a
1.5-inch SO-DIMM. The top slot can accommodate a 2.0-inch SO-DIMM.
Note
Future devices with higher density may allow expansion
beyond the current 128-MB limit.
Mechanical Design of RAM SO-DIMMs
4
The mechanical characteristics of the RAM expansion SO-DIMM are given in
the JEDEC specification for the 144-pin 8-byte DRAM SO-DIMM. The
specification number is JEDEC MO-190; it is available from the Electronics
Industry Association’s web site, at
The specification defines SO-DIMMs with nominal heights of 1.0, 1.25, 1.5, or
2.0 inches. The iMac computer can accommodate two 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 iMac, 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
The specification defines several attributes of the DIMM, including storage
capacity and configuration, connector pin assignments, and electrical loading.
The specification supports SO-DIMMs with either one or two banks of memory.