Windows 7 has both. You can either try a 32 bit operating system or a 64 bit operating system. You should careful select the operating system that will suite you requirement. In simple words, 64 bit Operating system is more advanced than 32 Bit operating system. If you do not select the correct operating system, you may face compatibility problems. It depends on your choice operating system that whether you get full performance from your system.

There will be no advantage if you run a 32 bit software in a 64 bit environment. So it is one of your primary concerns that you should decide that which software you are going to use with the operating system. The main advantage of 64 bit operating system and processor is that it can handle more memory. A 32 bit processor can acknowledge only 4 GB RAM, where as a 64 bit Operating system can address 17,179,869,184 GB (16 Exabytes) of RAM. So if you are using 4 GB + RAM it is better that you use a 64 bit operating system.