Abstract
This paper describes the motivation architecture and performance of SPIN an extensible operating system SPIN provides an extension infrastructure together with a core set of extensible services that allow applications to safely change the operating systems interface and implementation Extensions allow an application to specialize the underlying operating system in order to achieve a particular level of performance and function ality SPIN uses language and linktime echanisms to inexpensively export negrained interfaces to operating system services Extensions are written in a type safe language and are dynamically linked into the operating system kernel This approach oers extensions rapid access to system services while protecting the operating system code executing within the kernel address space SPIN and its extensions are written in Modula and run on DEC Alpha workstations Introductio