My mobo is Bio* TZ77XE4. I have two pairs (four modules) of http://www.newegg.com/Product/Product.aspx?Item=N82E168... Now for four modules: Only manual 1600 MHz works. XMP or manual 1800/1866 will show errors on Memtest86. For two modules 1866 MHz works under XMP1. I don't change CPU settings. Any way I can get all four modules to 1866? FYI the SPD is only 1333.
XMP profiles are not guaranteed to work when using unmatched memory sticks. Since you're running two separate pairs of matched memory rather than one set of 4 matched sticks it's entirely possible that the memory will not run at that speed using the XMP profile settings.
Most of the time this can be solved by bumping up the DRAM voltage by .05 volts, try that
EDIT: The SPD contains a number of JEDEC profiles which are industry standardized speeds (typically 400,533,667 Mhz bus speed) so 1333MT/s (667Mhz) is the highest standard speed that will be automatically selected. The SPD also contains XMP profiles (typically 800, 900, 933, 1000, 1066) which are overclocked profiles that will not be selected by default
which is what would work for 2 modules but not 4. Value level motherboards such as the TZ77XE4 often don't have the high quality components necessary to ensure that 4 or even 8 modules will be stable with settings set for 2 modules.
Ergo, 1.65 volts might be enough for 2 DIMMs at 1866 on a Biostar board and 8 DIMMs on an Asus Rampage IV Extreme but 4 DIMMs on the same Biostar board might require 1.7 volts or even looser timings. You get what you pay for
Well it's rated at 1.65V so when put in pairs or when run on a very good motherboard that's all that it will need. However, most DDR3 modules can also run at 1.5 volts (JEDEC specification) and up to around 1.9 volts at the absolute max with stable operating frequencies dependent on supply voltage and other factors.
Intel's internal engineering for the 32mn Sandybridge processor allows for DRAM voltages up to an absolute maximum of 1.85 volts (I am not sure what it is for the 22nm Ivybridge), however 1.5 volts is standard with 1.65 volts to 1.7 volts being the practical upper maximum for most enthusiasts who don't mind 300 dollar paperweights.
If 1.7 volts is stable then you should be fine. Keep in mind however that your motherboard is a bit of an under performer in this respect and you may run into problems in the future