title: How many physical channels SATA controller has?
body: <p>Imagine a system with one SATA controller. If controller operates in IDE mode it will show up in device manager like this:</p>
  
  <p>Windows XP:</p>
  
  <pre><code>IDE controller's name
  Primary IDE Channel
  Secondary IDE Channel
  </code></pre>
  
  <p>Windows >= Vista:</p>
  
  <pre><code>IDE controller's name
  ATA Channel 0
  ATA Channel 1
  </code></pre>
  
  <p>And if controller operates in AHCI mode it will show up like "SATA AHCI controller" on both XP and >= Vista.</p>
  
  <p>SATA controller in AHCI mode supports up to 32 devices (32 bit mask indicates device connection). I think it is just software limitation, given that each device requires separate channel, it is unlikely that such system exist where SATA controller is "wired" with all 32 channels. But I think 32 is a number that implies that controller can deal with more than two devices and thus has more than two channels. So, I want to ask how many channels SATA controller often has in practice. ATA controller has two channels, so does it mean that SATA controller has the same number of channels for software compatibility in IDE mode? Or maybe it has more than two channels, but in IDE mode only first two channels will be available? (at least on XP because "primary" channel and "secondary" channel greatly reduce the possibility of "third" channel which is not the case with "0" channel, "1" channel, "2" channel and so on)</p>