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　服务简介

　几乎每一个操作系统都有一种在系统启动时刻启动进程的机制，这些进程提供了一些不依赖于任何用户交互式的服务。在Windows中，这样的进程称为服务。在桌面Windows系统中，服务程序由三个组件构成的：服务应用、服务控制程序(SCP)和服务控制管理器(SCM)。(以上参见《深入解析Windows操作系统》第四版第四章第二节。)

　桌面系统的服务机制是非常复杂的，至少看的我现在还在晕。在嵌入式系统中，当然不会如此复杂。

　Windows CE 5.0服务程序在系统架构中的位置如下图，Services.exe是作为服务DLL文件的宿主，提供开始、暂停和停止服务的能力。服务和驱动(主要由Device.exe加载)有个很有意思的关系，从本质上说它们是一回事。

　下图是Windows Mobile 6.0 Professional模拟器Services.exe和Device.exe进程加载的DLL文件的截图：

　Windows CE 6.0服务程序在系统架构中的位置，微软把驱动分为用户模式和内核模式：

　进一步详细的看下Windows CE 6.0的用户态：

　ServicesD.EXE用于服务的宿主，UDevice.EXE用于用户态驱动的宿主。

　"ServicesD.exe is a process that supplements the Udevice.exe process. ServicesD.exe provides enhanced loading capabilities such as support for starting, pausing, and stopping services. The programming model for writing services and writing device drivers is very similar in Windows Embedded CE. You can develop a server that runs on Udevice.exe rather than on ServicesD.exe, with identical code, provided that your server does not require advanced features offered by ServicesD.exe. “

　再详细看一下Windows CE 6.0的内核态：

　"DEVMGR.DLL is the Device Manager that is loaded by the kernel, it runs continuously, and it manages loaded device drivers and their interfaces. When the Device Manager loads, it also loads the I/O Resource Manager to read a list of available resources from the registry. “