title: Device drivers and Windows
body: <p>I am trying to complete the picture of how the PC and the OS interacts together. And I am at point, where I am little out of guess when it comes to device drivers. </p>
  
  <p>Please, don´t write things like its too complicated, or you don´t need to know when using high programming laguage and winapi functions. I want to know, it´s for study purposes.</p>
  
  <p>So, the very basic structure of how OS and PC (by PC I mean of course HW) is how I see it is that all other than direct CPU commands, which can CPU do on itself (arithmetic operation, its registers access and memory access) must pass thru OS. Mainly becouse from ring level 3 you cannot use in and out intructions which are used for acesing other HW. I know that there is MMIO,but it must be set by port comunication first.</p>
  
  <p>It was not like this all the time. Even I am bit young to remember MSDOS, I know you could access HW directly, becouse there ws no limitation, no ring mode. So you could to write string to diplay use wheather DOS function, or directly acess video card memory and write it by yourself. </p>
  
  <p>But as OS developed, there is no longer this possibility. But it is fine, since OS now handles all the HW comunication, and frankly it more convinient and much more safe (I would say the only option) in multitasking environment. So nowdays you instead of using int instructions to use BIOS mapped function or DOS function you call dll which internally than handles everything you don´t need to know about.</p>
  
  <p>I understand this. I also undrstand that device drivers is the piece of code that runs in ring level 0, so it can do all the HW interactions. But what I don´t understand is connection between OS and device driver. Let´s take a example - I want to make a sound card make a sound. So I call windows API to acess sound card, but what happens than? Does windows call device drivers to do so? </p>
  
  <p>But if it does call device driver, does it mean, that all device drivers which can be called by winAPI function, must have routines named in some specific way? I mean, when I have new sound card, must its drivers have functions named same as the old one? So Windows can actually call the same function from its perspective? But if Windows have predefined sets of functions requored by device drivers, that it cannot use new drivers that doesent existed before last version of OS came out. </p>
  
  <p>Please, help me understand this mess. I am really getting mad. Thanks.</p>