Common Language Infrastructure

The Common Language Infrastructure (CLI) is an open specification (technical standard) developed by Microsoft and standardized by ISO and ECMA that describes executable code and a runtime environment that allows multiple high-level languages to be used on different computer platforms without being rewritten for specific architectures. This implies it is platform agnostic. The .NET Framework and the free and open source Mono and Portable.NET are implementations of the CLI.

Among other things, the CLI specification describes the following four aspects:

All compatible languages compile to Common Intermediate Language (CIL), which is an intermediate language that is abstracted from the platform hardware. When the code is executed, the platform-specific VES will compile the CIL to the machine language according to the specific hardware and operating system.

In August 2000, Microsoft, Hewlett-Packard, Intel, and others worked to standardize CLI. By December 2001, it was ratified by the ECMA, with ISO standardization following in April 2003.

Microsoft and its partners hold patents for CLI. ECMA and ISO require that all patents essential to implementation be made available under "reasonable and non-discriminatory (RAND) terms." It is common for RAND licensing to require some royalty payment, which could be a cause for concern with Mono. As of January 2013, neither Microsoft nor its partners have identified any patents essential to CLI implementations subject to RAND terms.

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