REX OS

{{Short description|Real-time operating system}}

{{Update|updated=2012|date=May 2023}}

{{Infobox OS

| name = REX Operating System

| logo =

| caption = REX Operating System

| screenshot =

| developer = Qualcomm

| source_model = Proprietary

| kernel_type = Microkernel RTOS

| supported_platforms = ARM

| family = L4A Pistachio and Iguana embedded operating system

| released = {{Start date and age|1999}}{{cite web |url=http://wenku.baidu.com/view/cbe622fbaef8941ea76e05e7.html |title=REX and Common Software |author= |access-date=2012-03-10}}

| discontinued = Yes

| latest_release_version =

| latest_release_date =

| working_state = Discontinued

| license = Proprietary

| marketing_target = Smartphones

| programmed_in = C

| language =

| update model =

| package_manager =

| website =

}}

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.{{cite web |url=http://tjworld.net/wiki/Android/HTC/Vision |title=HTC Vision |access-date=2012-03-12 |author=Edgewall Software}}

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.{{cite book |last=Asif |first=Saad Zaman |date=2011-01-11 |title=Next Generation Mobile Communications Ecosystem: Technology Management for Mobile Communications |publisher=John Wiley and Sons |page=299}}

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.