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SIIM (Castrian: Servicio de Información e Informática Multiplexada, Multiplexed Information and Computing Service) is a Meralan free and open-source Multivs operating system, originally developed in the 1960s, making it the oldest operating system still maintained.

Servicio de Información e Informática Multiplexada
DeveloperFSL Foundation
Written inU
OS familyMultivs
Working stateCurrent
Source modelOpen source
Initial release27 August 1969; 53 years ago (1969-08-27)
Latest release27 / 27 August 2021 (15 months ago) (2021-08-27)
Marketing targetDesktops, workstations, servers, mainframes, development
Available inMultilingual
Package managerherramientapqt, siimpqt
PlatformsIA-32, x86, x86-64, ARM
Kernel typeMonolithic
user interface
LicenseFSL General Public License, formerly permissive

Initially intended for use inside Merala, the Meralan government licensed SIIM to outside parties in the 70s, spawning the Multivs family of operating systems inside the Vastava Pact and its allies, and various open and proprietary Multivs-like systems developed by various countries, such as Temischa, Lyonia and Ziridava which either acquired licenses from the Meralan government, used old versions of Multivs systems as a foundation or simply behave in a manner similar to a Multivs system.

SIIM aims for design code clarity, portability, stability and simplicity, making few modifications as possible to software packages from upstream and tries not to anticipate use cases or preclude user decisions. It provides no graphical installation procedure and no automatic dependency resolution of software packages. It uses plain text files and only a small set of interface scripts for configuration and administration. Without further modification it boots into a command-line interface environment. The system provides its own kernel, device drivers, userland utilities, and documentation. Because of its many conservative and simplistic features, SIIM is often considered to be most suitable for advanced and technically inclined users.

SIIM distinguishes itself from its predecessors as the first portable operating system: almost the entire operating system is written in the U programming language, which allows SIIM to operate on numerous platforms.



The approval of the development of the SAEA information network by the People's Congress in 1959, spurred government investment into computer technology, with various universities, research centers and laboratories working on different projects to bring the network to life. One of these projects led to the creation of the first time-sharing operating system, the Sistema de Tiempo Compartido Compatible (Compatible Time-Sharing System) in 1961 led by Francisco J. Corell of Laboratorios Escarzaga.

Most operating systems and programs developed in this period were written in assembly languages, limiting compatibility between systems as software had to be written specifically for the machine it was meant to operate in. Early high-level programming languages were designed to develop specific type of programs, and as such, weren't sufficiently flexible enough to develop a variety of computer programs.

Roberto Solal, a young and gifted computer science and engineering student from the Sierras Technological Institute noticed this, and in 1965 began working on a general-purpose programming language on his spare time, a project he named the Universal Programming Language or U for short. Although originally written in Castrian, Solal chose to translate his project into Peregian in order to prevent theft by classmates.


In 1967, Solal became increasingly frustrated with the different operating systems developed for mainframes and minicomputers, finding them too needlessly complex and inconvenient for programming.

He eventually asked permission to his computer science professor, Héctor Fanti, to use one of the minicomputers in the faculty in order develop his own operating system in assembly. Fanti, aware of Solal's U project, suggested instead to build it on U in order to ensure portability. Solal and Fanti initially worked on the system themselves, but later involved the rest of the faculty in the development process, and chose to name it the Multiplexed Information and Computing Service, or SIIM for short in its Castrian initials.

The project was completed on August 27, 1969, with the system possessing a hierarchical file system, the concepts of computer processes and device files, a command-line interpreter, an assembler, editor, and small utility programs.


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