rtos

from The Free On-line Dictionary of Computing (8 July 2008)

Real-Time Operating System
RTOS

   <operating system> (RTOS) Any {operating system} where
   interrupts are guaranteed to be handled within a certain
   specified maximum time, thereby making it suitable for control
   of hardware in {embedded systems} and other time-critical
   applications.  RTOS is not a specific product but a class of
   operating systems.

   [Other criteria?]

   (1998-02-27)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

RTOS
       Real Time Operating System (OS, Interdata, Prime, ...)