Vulkan is an explicit API, enabling direct control over how GPUs
actually work. As such, Vulkan supports systems that have multiple
GPUs, each running with a different driver, or ICD (Installable Client
Driver). Vulkan also supports multiple global contexts (instances, in
Vulkan terminology). The ICD loader is a library that is placed
between a Vulkan application and any number of Vulkan drivers, in
order to support multiple drivers and the instance-level functionality
that works across these drivers. Additionally, the loader manages
inserting Vulkan layer libraries, such as validation layers, between
an application and the drivers.