This article needs to be updated. Please help update this article to reflect recent events or newly available information. Last update: 2012 (May 2023)
REX Operating System
Written inC[1]
OS familyL4A Pistachio and Iguana embedded operating system
Working stateDiscontinued
Source modelProprietary
Initial release1999; 25 years ago (1999)[1]
Marketing targetSmartphones
Kernel typeMicrokernel RTOS

The REX Operating System (Real-time Executive Operating System) is a real-time operating system (RTOS) developed by Qualcomm for the ARM processor based mobile phone Dual-Mode Subscriber Station (DMSS) or Advanced Mode Subscriber Software (AMSS) development. As of 2007, most Korean cell phones ran on REX.

REX is a combination of two operating systems: L4Ka::Pistachio embedded microkernel and Iguana, with extensive modifications and extensions by Qualcomm and HTC.[2]

Originally developed for the Intel 80186, it was then ported to ARM, and x86 architectures are no longer supported. REX is not POSIX compliant or open-source software and requires a proprietary software license from Qualcomm for use.[3]

It seems not to be actively developed or marketed as of 2012, but is used in currently or recently sold low end cell phones, typically for use by pay-as-you-go customers, like the Samsung SPH-M300.


REX is an RTOS with the following features:

REX provides no memory protection features but does have memory management abilities.


  1. ^ a b c "REX and Common Software". Retrieved 2012-03-10.
  2. ^ Edgewall Software. "HTC Vision". Retrieved 2012-03-12.
  3. ^ Asif, Saad Zaman (2011-01-11). Next Generation Mobile Communications Ecosystem: Technology Management for Mobile Communications. John Wiley and Sons. p. 299.