a) For initial development, start with a PC / workstation with a 1GB or 2GB GTX560 card; this uses the latest Fermi GPU with L1/L2 caches, uses a maximum of 170W, will fit into most PCs (though it is a long PCIe card and two slots wide), and costs around £200 from suppliers such as dabs.com. For the best performance, put it in a workstation with a 16x PCIe gen 2 slot.

Note that the GTX560 is quite big (which could be a problem in a small computer case) and requires two 6-pin connectors (see notes below about this). If this is a problem, then one can start with the GT440 card (£70 from dabs.com) which is not as long, and appears not to use any 6-pin power connectors.

b) If double precision floating point arithmetic is important, consider the new Quadro 4000 which has much better double precision performance than the GTX cards in which the double precision performance is only 1/8 of the single precision performance.

c) For production computing, move to S2050 Tesla servers; these have 4 GPUs in a 1U server, each with 3GB graphics memory. They also use the Fermi GPU and are produced by NVIDIA with tighter quality control, but note that they do not provide any video output. I suggest using the SuperMicro Twin2 as the host system; each of its four independent compute nodes can connect to half of a S2050, and they also come with QDR Infiniband to form a tightly-coupled GPU compute cluster. See also Supermicro's new GPU servers in which two Tesla GPUs are housed within a 1U server.

d) HP has the HP SL6500 Scalable System which is a 4U unit which can hold 4 compute nodes, each with 3 M2050/2070 GPUs and QDR Infiniband.

e) Dell has the PowerEdge C410x PCie expansion chassis which is a 3U unit which can hold up to 16 GPUs to be connected to 1-4 separate compute nodes.

Power connectors for NVIDIA cards

All of NVIDIA's high-end cards require one or more PCI Express power connectors. These come in two flavours, 6-pin and 8-pin. Some low-end cards require just one 6-pin connection, while the most powerful card requires two 8-pin connections. It used to be difficult to find out what each card used, but now you can find out by going to this GeForce family page, selecting the card of interest, and then the Specifications tab, and then scrolling to the bottom.

Most new power supplies offer at least one 6-pin connection, and quite a few provide an 8-pin connection.

A lot of graphics cards come with adapters to convert the connections offered by an existing power supply to what you need. In particular, the GTX560 may come with an adapter like this to convert two 4-pin molex supplies (for disk drives) into one 6-pin PCI Express connector. This enables you to install the GTX560 in a system which has a power supply with only one 6-pin connector.