I heard that it would be best to pair memory in an iMac G5. Did some googling and turned up [link|http://forums.macrumors.com/archive/index.php/t-90654|this post by Elan0204](about 1/3rd down the page)

... the German site PPCNUX provides benchmarks for a 1.8GHz iMac G5 using XBench 1.1.3. Specifically, the benchmarks compare an iMac G5 with two unmatched DIMMs totaling 1.25GB of memory to the same iMac with two matched 512MB DIMMs (for a total of 1GB). Even though the former system had more RAM, the "matched" system returned significantly better results:

System Fill:
Unmatched: 1625.25
Matched: 2231.49
...

Found the [link|http://www.ppcnux.de/modules.php?name=News&file=article&sid=4092|chart] on PPCNUX.

Apparently [link|http://www.macbidouille.com/downloads/testbusG5us.sit|http://www.macbidoui...s/testbusG5us.sit] will test if your system is in 64 or 128 bit mode.

Found [link|http://developer.apple.com/documentation/Hardware/Developer_Notes/Macintosh_CPUs-G5/iMacG5/04_Expansion/chapter_5_section_1.html|this] on Apple's site

This chapter describes the DDR SDRAM expansion features of the iMac G5 computer.
...
The throughput of the 400 MHz memory bus is dependent on the DIMMs installed. If only one DIMM is installed, the memory bus is 64-bit. If two non-identical DIMMs are installed, there are two 64\ufffdbit memory buses. If two identical DIMMs are installed, the memory bus is 128-bit. Identical DIMM pairs have the same size and composition and provide the fastest and most efficient throughput.

Darrell Spice, Jr.                      [link|http://www.spiceware.org/cgi-bin/spa.pl?album=./Artistic%20Overpass|Artistic Overpass]\n[link|http://www.spiceware.org/|SpiceWare] - We don't do Windows, it's too much of a chore

The iMac G5 has 3 modes depending on how the memory is installed


• single channel 64 bit - one RAM slot filled
  
  
• dual channel 64 bit - both slots filled w/mismatched memory
  
  
• single channel 128 bit - both slots filled w/matched memory
  

From [link|http://www.ppcnux.de/modules.php?name=News&file=article&sid=4092|here](German - read the , in the numbers as . )

Xbench Memory Test iMac G5 1,8GHz - in MB/s
Konfiguration	64Bit - 256MB	128Bit - 1GB	2x64Bit - 1,25GB
System Fill	1664,16	2231,49	1625,25
System Copy	750,36	1041,32	861,25
Stream Copy	1217,79	1615,10	1255,89
Stream Scale	1250,43	1657,52	1251,27
Stream Add	1439,19	1781,15	1423,78
Stream Triad	1461,27	1794,59	1441,01

The results for single channel 64 and dual channel 64 are very close, and they both are trounced by single channel 128 bit access.

I haven't kept up with memory technology, does the consumer PC have 128 bit memory access like the consumer Mac?

Darrell Spice, Jr.                      [link|http://www.spiceware.org/cgi-bin/spa.pl?album=./Artistic%20Overpass|Artistic Overpass]\n[link|http://www.spiceware.org/|SpiceWare] - We don't do Windows, it's too much of a chore