resources such as files, I/O devices, users, and processes are all represented as virtual files in the namespace served by their managing process. Key servers in Helios are the previously mentioned loader, processor manager and network server, together with the session manager, the window server and the file server. Others include the keyboard, mouse, RS-232 and Centronics servers (built into the host I/O server), the null server (like Unix's /dev/null), and the logger server (like Unix's syslog). Programming and utilities From a user's perspective, Helios is quite similar to Unix. Most of the usual utility programs are provided, some with extensions to reflect the availability of multiple machines. What is not immediately apparent is that Helios extends the notion of Unix pipes into a language called Component Distribution Language (CDL). In CDL, a typical Unix shell pipeline such as is called a task force, and is transparently distributed by the Task Force Manager server across the available CPUs. CDL extends traditional Unix syntax with additional operators for bi-directional pipes, sequential and parallel process farm operators, load balancing and resource management. Helios applications can be written using C, C++, FORTRAN and Modula-2. The POSIX library assists in porting existing Unix software, and provides a familiar environment for programmers. Helios does not support programs written in the occam programming language. Hardware Helios was predominantly intended to be used with Transputer systems. It is compatible with products from various manufacturers including INMOS' TRAM systems, the Meiko CS, Parsytec MultiCluster and SuperCluster, and the Telmat T.Node. The Atari Transputer Workstation was perhaps the highest profile Helios hardware, at least outside academia. Helios can run on T4xx and T8xx, 32-bit Transputers (but not the T2xx 16-bit models) and includes device drivers for various SCSI, Ethernet and graphics hardware from Inmos, Transtech, and others. In its later versions, Helios was ported to the TI TMS320C40 DSP and to the ARM architecture, the latter used by the Active Book tablet device. References Further reading External links Ram Meenakshisundaram's Transputer Home Page Transputer.net Helios Library Distributed operating systems Microkernel-based operating systems Unix variants 1988 software