The Janus supercomputer is a modular, massively parallel, and reconfigurable FPGA-based computing system for High Performance Scientific Computing.
It takes the name from the ancient Roman god of gates and doors, of beginnings and endings, of passages and time, usually represented by two faces, one looking to the past, another one to future.
After a gestation period of around two years, Janus was born in 2008 thanks to a very successful scientific collaboration between researchers from BIFI and the Universidad de Zaragoza, Universidad Complutense de Madrid, Universidad de Extremadura, Università degli Studi di Roma "La Sapienza" and Università di Ferrara.
Its reconfigurable architecture would permit Janus to afford different scientific computational applications, as in Physic, in Chemistry or in Biology. So far, the Janus Collaboration focused its efforts on the study and simulation of spin glasses, paradigm of complex systems.
From the innovative work by Pearson and Richardson[1] in the late 70’s or that of Ogielsky and Condon[2] in the 80’s to our days, profiting of the newest technological advances, several refined dedicated computers and improved clusters have been developed to study spin glasses. Two successful examples can be found also in Zaragoza. In 1991 the group of Zaragoza designed and developed RTN (Reconfigurable Transputer Network)[3]. Later on, a second generation spin glass machine was completed in 2000 and called SUE (Spin Update Engine)[4].


Janus is composed by 16 boards. On each board, a bidimensional 4x4 grid of FPGA-processors is located and linked obeying periodic boundary conditions. Each of these processors is called SP (Simulation Processor) and carries on the simulations.  A 17th FPGA is settled in the middle acting as a crossbar and called IOP (Inpu/Output Processor), in charge of all internal connections and external communications. All FPGA modules are Xilinx Virtex4-LX200.


The Janus Operating System (JOS) is compatible with any Linux-based platform. It comprises three parts:
  • JOSlib: libraries in Perl and C to control IOP devices),

  • josd: multiuser environment for resource abstraction and concurrent jobs management)

  • jlib: set of SP firmware modules for scientific applications and C libraries to control them via the josd.


All SP's in Janus are reprogramed using the VHDL language.
For a more detailed explanation regarding the Hardware and Software of Janus, you may like to have a look to references[5], [6] and [7] below.
As we mentioned above, during the whole Janus' life the Janus Collaboration has devoted its time and efforts to the simulation of spin glasses. It can be said that after 6 years Janus still maintains its edge over the World wide spin glasses simulations, reaching simulation times up to 0.1 seconds of a real experiment, very large lattice size, very low temperatures and a huge amount of samples. As a consequence, all Janus work has deserved several publications in different outstanding scientific journals, as Physical Review Letters or the Proceeding of the National Academy of Science.
In order to see a complete list of the Janus Collaboarribaration publications, please visit the Publication Sectarribaion of Janus and JanusII.