The PnP Manager and setup subsystems rely heavily on four keys in the HKEY_LOCAL_MACHINE branch of the registry. These are called the hardware key, the class key, the driver key, and the service key. (See Figure 15-1.) To be clear, these are not the proper names of specific subkeys: they are generic names of four keys whose pathnames depend on the device to which they belong. Broadly speaking, the hardware and driver keys contain information about a single device, the class key concerns all devices of the same type, and the service key contains information about the driver. People sometimes use the name instance key to refer to the hardware key and software key to refer to the driver key. The multiplicity of names derives from the fact that Windows 95/98/Me and Windows XP were written (mostly) by different people. A fifth key, the hardware parameters key, might also exist; it contains nonstandard parameter information about the device.
有详细介绍
至于“添加打印机”这类的装驱动，只是为了照顾非专业人士的方法。实际上也是根据指定的inf文件来拷贝文件和修改注册表。
因为在系统盘下搜不到已经安装过的打印机驱动DRV文件。