| Developer | Qualcomm | 
|---|---|
| Written in | C[1] | 
| OS family | L4A Pistachio and Iguana embedded operating system | 
| Working state | Discontinued | 
| Source model | Proprietary | 
| Initial release | 1999[1] | 
| Marketing target | Smartphones | 
| Platforms | ARM | 
| Kernel type | Microkernel RTOS | 
| License | Proprietary | 
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.
Features
REX is an RTOS with the following features:
- Preemptive multitasking
 - Task management
 - Task synchronization
 - Exclusive lock
 - Timer
 - Interrupt management
 - Uses less than 5K of ROM[1]
 
REX provides no memory protection features but does have memory management abilities.
References
- 1 2 3 "REX and Common Software". Retrieved 2012-03-10.
 - ↑ Edgewall Software. "HTC Vision". Retrieved 2012-03-12.
 - ↑ Asif, Saad Zaman (2011-01-11). Next Generation Mobile Communications Ecosystem: Technology Management for Mobile Communications. John Wiley and Sons. p. 299.
 
External links
- Iguana Archived 2006-04-26 at the Wayback Machine
 - L4 Based Operating Systems Archived 2018-06-14 at the Wayback Machine
 - NICTA L4-embedded Kernel Archived 2014-02-27 at the Wayback Machine
 - Qualcomm Corporate Site