Developer Documentation
PATHHardware Documentation > Original Power Mac G3 Computers Developer Note


RAM DIMMs

The logic board has three DRAM expansion slots. The DRAM expansion slots accept 3.3 volt unbuffered 8-byte (x64 non-parity) SDRAM DIMMs. The 8-byte 168-pin DIMM has a 64-bit-wide data bus per bank. One of the slots contains a factory installed SDRAM DIMM.

The mechanical design of the SDRAM DIMM is defined by the JEDEC MO-161 specification.

The JEDEC MO-161 specification can be found at

http://www.jedec.org/download/freestd/pub95/mo161c.pdf

The electrical characteristics of the SDRAM DIMM are defined by the JEDEC standard 21-C section 4.5.4 release 8. The specification can be found at

http://www.jedec.org/download/freestd/pub21/4_5_4-R8.PDF

The minimum bank size supported by the Grackle IC is 2 MB, and the largest is 64 MB; the largest DIMM supported is a 4-bank DIMM of 256 MB using 128 Mbit SDRAM devices. Table 1 shows the DIMM configurations and sizes for a range of SDRAM device sizes that are supported on the logic board.

Table 4-1 Memory configurations and sizes for SDRAM DIMMS 

Device size

Device
configuration

Devices
per bank

DIMM size
per bank

Maximum DIMM size

16 Mbits 256K x 32 x 2 2 4 MB 16 MB
16 Mbits 2 Mbits x 4 x 2 16 32 MB 32 MB
16 Mbits 1 Mbits x 8 x 2 8 16 MB 32 MB
16 Mbits 512K x 16 x 2 4 8 MB 32 MB
64 Mbits 1 Mbits x 32 x 2 2 16 MB 64 MB
64 Mbits 512K x 32 x 4 2 16 MB 64 MB
64 Mbits 8 Mbits x 4 x 2 16 128 MB 128 MB
64 Mbits 4 Mbits x 4 x 4 16 128 MB 128 MB
64 Mbits 4 Mbit x 8 x 2 8 64 MB 128 MB
64 Mbits 2 Mbits x 16 x 2 4 32 MB 128 MB
64 Mbits 1 Mbits x 16 x4 4 32 MB 128 MB
128 Mbits 4 Mbits x 8 x 4 8 64 MB 256 MB
128 Mbits 16 Mbits x 8 4 64 MB 256 MB

The SDRAM DIMMs can be installed one or more at a time. The Power Macintosh G3 logic board supports only linear memory organization; therefore no performance gains are seen when two DIMMs of the same size are installed. Any supported size DIMM can be installed in either DIMM slot, and the combined memory of all of the DIMMs installed will be configured as a contiguous array of memory.

IMPORTANT
The modular desktop enclosure accommodates SDRAM DIMMs of 1.15 inches in height. The All-in-one and tower enclosures accommodate RAM DIMMs of 1.5 inches in height.

Presence Detect EEPROM

SDRAM Devices


© 1998 Apple Computer, Inc. - Revised 8/13/98