The memory modules are provided on a PCB with a passive heatsink (heatspreader), which is supposed to enhance the memory cooling also with higher frequencies and/or higher voltages. Thus one can achieve a longer life-time and better overclocking results, whereby for oc’ing higher voltages are necessary. These modules are officially designed for a JEDEC standard voltage of 1.50 Volt for DDR3 modules.

Not the full 4GB during booting, but only 3GB in the BIOS or operating system …

Depending on the operating system and/or BIOS setting, it can occur that the memory capacity is only indicated as approx. 3GB instead of the 4GB. 4GB RAM size or any memory size over 2GB is still a case sui generis.Here at ocinside.de is a guide which contains among other things a table, how much RAM is supported by operating systems.