User:Jojoyee/sandbox

Framework transitions
Early versions of HarmonyOS, starting from version 1.0, employed a "kernel abstraction layer" (KAL) subsystem to support a multi-kernel architecture. This allowed developers to choose different operating system kernels based on the resources available on each device. For low-powered devices such as wearables and Huawei's GT smartwatches, HarmonyOS utilized the LiteOS kernel instead of Linux. It also integrated the LiteOS SDK for TV applications and ensured compatibility with Android apps through the Ark Compiler and a dual-framework approach. HarmonyOS 1.0's original L0-L2 source code branch was contributed to the OpenAtom Foundation to accelerate system development.

HarmonyOS 2.0 introduced a modified version of OpenHarmony's L3-L5 source code, expanding its compatibility across smartphones and tablets. Underneath the kernel abstraction layer (KAL) subsystem, HarmonyOS used the Linux kernel and the AOSP codebase. This setup enabled Android APK files and App Bundles (AAB) to run natively, similar to older Huawei EMUI-based devices, without needing root access.

Additionally, HarmonyOS supported native apps packaged for Huawei Mobile Services through the Ark Compiler, leveraging the OpenHarmony framework within its dual-framework structure at the System Service Layer. This configuration allowed the operating system to run apps developed with restricted HarmonyOS APIs.

Until the release of HarmonyOS 5.0, known as HarmonyOS NEXT, using its microkernel within a single framework, the operating system employed a dual-framework approach for Huawei's HarmonyOS devices with the AOSP codebase.

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On smartphones and tablets since HarmonyOS 2.0 introduced the modified OpenHarmony L3-L5 source code clone as part of device ecosystem expansion, until the newer native single framework HarmonyOS 5.0 version with HarmonyOS NEXT Galaxy Edition iteration, it contained a dual-framework system in its convergence stages of legacy Huawei Android powered devices, HarmonyOS ran with the Linux kernel underneath the kernel abstraction layer (KAL) subsystem. The userland was used on AOSP codebase as a base for the EMUI system launcher to run APK apps natively, without root support just as with older Huawei EMUI-based smartphones. In addition, the OS supports native HarmonyOS apps in app packages on devices with Huawei Mobile Services via Ark Compiler, with the OpenHarmony layer of HarmonyOS framework under the dual framework in the System Service Layer. While incorporating the OpenHarmony layer for running the APP files developed based on limited developing HarmonyOS APIs, the operating system utilizes the Linux Kernel Abstract Layer (KAL) subsystem with the AOSP code modified with the EMUI user interface in the userland to allow for compatibility with Android APK files and App Bundles (AAB), enabling them to be seamlessly published on AppGallery and native third-party Google Mobile Services workarounds on AOSP framework side during transition convergence period.