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 applica
tions 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 mechanisms to
inexpensively export negrained interfaces to operat
ing system services Extensions are written in a type
safe language and are dynamically linked into the op
erating system kernel This approach oers extensions
rapid access to system services while protecting the op
erating system code executing within the kernel address
space SPIN and its extensions are written in Modula
and run on DEC Alpha workstations
Introductio