Audio Impressions' Realtime Instruments is a comprehensive package of ten sample libraries, which are powered by DVZ RT. These libraries include Orchestral, Band, World, Keyboards, Guitars, Drum Kits, Music Effects, Harps, Baroque & Antique Instruments, Les Grandes Orgues (Pipe Organs).

Realtime Instruments uses a distributed / clustered computing approach whereby you have one "DVZ RT control computer", multiple "Sampler" computer's, each running Native Instruments' Kontakt sampler, and your existing computer running your sequencer of choice hosting the Ai plug-in - VST on Windows, AU on Mac OS X - which communicates with the other computers via Gigabit ethernet (ReWire and an additional AI Panel application are also used).

Here's what the "DVZ RT control computer" does:

1. It provides the main Graphical User Interface (GUI) for selecting library instruments, patterns, effects, orchestrations and so forth. This is not done on the individual samplers, but is instead centrally controlled. You don't even need to connect keyboards, video monitors or mice to the samplers; use a KVM (Keyboard-Video Monitor-Mouse) switch to boot them and you can save space and money on peripherals.
2. It performs DVZ RT voice allocation, accomplishing the actual divisi so that notes played (from sequencer or directly from the music keyboard) are allocated to the various sections and players within each section. In this way, a MIDI track on one sequencer port and channel becomes multiple MIDI port and channel outputs which are then sent out via Ethernet to the various samplers.
3. It receives audio back from the various samplers via audio-over-Ethernet.
4. It processes that audio with Audio Impressions' "SPACE" software to provide placement of each player anywhere one desires within a virtual-performance environment, with that environment being scaleable and adjustable in real time and with realistic microphone bleed among all players so it sounds like they are actually performing at once in the same place.
5. It sends out the resulting audio in whatever format the user selects, from mono to stereo to 5.1 or 7.1, etc., via either an analog or digital output, which in turn can be fed to typical recording and/or monitoring destinations. Instead of having to buy a costly audio interface for each sampler, you need as few as just one audio interface.

This is explained in more detail in Audio Impressions' FAQ.

Realtime Instruments includes over 600 sampled instruments arranged in ten libraries (Complete PDF List), with most being solo players; in the case of the 70 orchestral string realtime players, 10 are soloists and thirty are 2-musician desks. The most comprehensive set of playing styles and effects for each instrument was recorded; all effects and styles appropriate to each instrument, such as mutes, bow positions, pizzicato, and flutter tongue are available at start up.

All Realtime Instruments samples were captured in "the world's finest recording studios" using "first-call players" and "the world's best instruments". These were recorded at the highest audio fidelity utilizing vintage Neumann and Telefunken tube condensers and ribbon mics, and silver-plated mic cables (completely bypassing studio patch bays); signals were recorded directly. No equalization, compression or other processing was used, instead sound was optimized through mic selection and placement.

To get an idea of what can be achieved, to play a full symphony orchestra or an equivalent number of instruments at 44.1 kHz or 48 kHz, you will need four sampler computers. Basically, with four samplers you can play the entire Realtime Instruments library at once, except for the guitars, drums, the pianos and the organ. Detailed system requirements / specifications can be found here.