在设备驱动层中使用了设备对象概念，屏蔽了驱动的具体实现，从而实现了跨平台。
In the device driven level, it shielded the implement details of drive with the concept of device object and achieved the cross platform of the graphic system.
PDD层的驱动则是根据具体的硬件设备和平台专门编写。
The PDD layer consists of the code that is specific to a given hardware device or platform.
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