Windows will use all the RAM it needs, unless you instruct it otherwise. There is a setting in msconfig to limit the amount of RAM, so just make sure that is not set.
System Manufacturer/Model Number Gateway/NV7923u & NV79C52u Laptops OS windows 7 professional & ultimate 64bit laptops CPU 2.27 boost to 2.53 & 2.53 boost to 2.80 Motherboard Mobile Intel® HM55 Express Chipset ??? Memory 4GB Graphics Card Intel® Graphics Media Accelerator HD Sound Card realtek High-definition audio support Monitor(s) Displays 17.3 " HD 1600 x 900
Hard Drives hatachi Travelstar 5400 500GB & west digital 500GB Internet Speed 35MB fios
Computer type PC/Desktop System Manufacturer/Model Number Alienware Aurora ALX R4 OS Windows 7 x64 (SP1) CPU Intel Core i7-3930K (3.2GHz, Turbo 4GHz) Motherboard Alienware Aurora-R4 x79 Memory 4x Samsung 4GB PC3-12800 DDR3 (16GB 1600MHz) Graphics Card Nvidia Geforce GTX 690 (Stock) Sound Card RealTek Integrated Audio Monitor(s) Displays Dell UltraSharp U3011 Screen Resolution 2560x1600
PSU 875W Some Dell PSU <.< Hard Drives Samsung P830 256 GB, WD Raptor 150GB, 2x 1TB HDDs Other Info Dell Inspiron Mini 10v (Intel Atom N270 1.6 GHz; 1GB; Windows 7 Ultimate)