According to Paul White of "Sound on Sound," the minimum system requirements for "Guitar Rig 1" for PC are 700 Mhz Pentium or 1.33 Ghz Athlon on Windows XP or later. For Mac, the minimum requirement is an 800 Mhz G3 running OS 9 or OS X.
"Guitar Rig" can be used as a complete stand-alone system or as a plug-in combined with other audio interfaces. Native Instruments' website lists the following supported interfaces: VST, Audio Units, RTAS, (Pro Tools 8 and higher), ASIO, Core Audio, DirectSound and WASAPI.
Native Instruments has kept "Guitar Rig" updated with new releases and versions. In 2011 the latest release is "Guitar Rig 4." Older versions of the software can be updated, but it is important to note the minimum system requirements for each release. The minimum requirements for "Guitar Rig 4" for PC are: Windows XP (latest Service Pack, 32 Bit), Windows Vista/Windows 7 (latest Service Pack, 32/64 Bit), Pentium 4 2.4 GHz or Intel Core Duo or AMD Athlon 64, 2 GB RAM. The minimum requirements for Mac are: OS X 10.5 or 10.6 (latest update), Intel Core Duo, 2 GB RAM.
Since "Guitar Rig" uses a computer to process audio signals in real time, it is imperative to minimize latency -- the delay of time taken to process the audio signal. Latency is a side-effect inherent in all digital audio signals to varying degrees. Computer sound cards measure latency in different ways, but one sure way to know your system has the lowest possible latency is to use a sound card that is ASIO compliant. ASIO is a standard, created by German software company, Steinberg, which bypasses the computer OS and allows the sound card, application and hardware to all communicate directly.