QsNet is the main (and only) product of Quadrics, a company that initially
started in the 1990s as the British firm Meiko that made parallel systems
called the Computer Surface 1 and 2. In the CS-2 a very good logarithmic
network was included that was made into a separate product after Meiko closed
down and the network part was taken over by the the Italian company Alenia and
put in the independent company Quadrics. The success came when Digital/Compaq
chose QsNet as the network for its large high-performance computer products,
the AlphaServer SC line. Some very large configurations of these machines were
sold, e.g., at the Pittsburgh Supercomputing Centre and the French CAE. QsNet
proved to be a very fast and reliable network and since about two years QsNet is
also offered for cluster systems.
Like Infiniband and Myrinet the network has effectively two parts: the ELAN interface cards, comparable to Infiniband Host Bus Adaptors or Myrinet's Lanai interface cards, and the Elite switch, comparable to an Infiniband switch/router or a Myrinet switch. The topology that is used is a (quaternary) fat tree like in most Infiniband switches, see Figure 5b for an example. The ELAN card interfaces with the PCI-X port of a host computer.
Ready-made Elite switches for clusters come in two sizes: with 16 and 128 ports but nothing in between. Of course one can put together networks for other sizes but this goes at the cost of compactness and speed. A difference with the other switches lies in the providing two virtual bi-directional channels per link. Since the end of 2003 Quadrics sells its second generation QsNet, QsNet II. The structure, protocols, etc., are very similar to those of the former QsNet but much faster: where in  a speed of 300 MB/s for an MPI Ping-Pong experiment was measured while QsNet II has a link speed of 1.3 GB/s. In this case the PCI-X bus speed is a limiting factor: it allows for somewhat more than about 900 MB/s. However, with the advent of PCI Express this limitation may be over. Also the latency for short messages has improved from ≅ 5 µs to 3 µs. Furthermore, the switch supports two priority levels which greatly helps in a fair distribution of message packets. This is more than Myrinet provides but less than the 16 priority levels of Infiniband. The in-switch latency is very low: about 35 ns.
Like Infiniband, QsNet(II) has RDMA capabilities that allow to write/read from/to
remote memory regions on the ELAN cards. This can however be extended to memory
regions of the host processor itself. So, in principle, one would be able to
view a QsNet-connected system as a virtual shared memory system. As yet, this
has not been realised nor on integrated systems, nor on clusters. Nevertheless,
it could be an attractive alternative for the much slower memory paged based
virtual shared memory systems like ThreadMarks
. A Cray-style
shmem library is offered that enables one-sided communication via
put and get operations.