Helios is a discontinued Unix-like operating system for parallel computers. It was developed and published by Perihelion Software. Its primary architecture is the Inmos Transputer. Helios' microkernel implements a distributed namespace and messaging protocol, through which services are accessed. A POSIX compatibility library enables the use of Unix application software, and the system provides most of the usual Unix utilities. Work on Helios began in the autumn of 1986. Its success was limited by the commercial failure of the Transputer, and efforts to move to other architectures met with limited success. Perihelion ceased trading in 1998. The name of the product was Helios. In the materials they produced, Perihelion Software never referred to the operating system as HeliOS. Development In the early 1980s, Tim King joined MetaComCo from the University of Bath, bringing with him some rights to an operating system called TRIPOS. MetaComCo secured a contract from Commodore to work on AmigaOS, with the AmigaDOS component being derived from TRIPOS. In 1986, King left MetaComCo to found Perihelion Software, and began development of a parallel operating system, initially targeted at the INMOS Transputer series of processors. Helios extended TRIPOS' use of a light-weight message passing architecture to networked parallel machines. Helios 1.0 was the first commercial release in the summer of 1988, followed by version 1.1 in autumn 1989, 1.1a in early 1990, 1.2 in December 1990 followed by 1.2.1 and 1.2.2 updates. Version 1.3 was a significant upgrade with numerous utility, library, server and driver improvements. The last commercial release was 1.3.1. Later Tim King and Nick Garnett gave permission to release the sources under the GNU Public License v3. Helios 1.4 Alpha was planned to include support for OpenLook, OpenMotif, KDE, Gnome, and X11R6 support for the Transputer, Linux, Solaris, and Windows. This release was not completed. Kernel and nucleus Helios was designed for a network of multiple nodes, connected by multiple high-bandwidth communications links. Nodes can be dedicated processing nodes, or processors with attached I/O devices. Small systems might consist of a host PC or workstation connected to a set of several processing nodes, while larger systems might have hundreds of processing nodes supported by dedicated nodes for storage, graphics, or user terminals. A Helios network requires at least one I/O Server node that is able to provide a file system server, console server and reset control for the processing nodes. At power on, the Helios