How many physical channels SATA controller has? - windows

Question

Imagine a system with one SATA controller. If controller operates in IDE mode it will show up in device manager like this:
Windows XP:
IDE controller's name
Primary IDE Channel
Secondary IDE Channel
Windows >= Vista:
IDE controller's name
ATA Channel 0
ATA Channel 1
And if controller operates in AHCI mode it will show up like "SATA AHCI controller" on both XP and >= Vista.
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)

Answer 1

A bit later but maybe would be useful for others.
Let's add some clarifications. There is SATA Host Controller with AHCI interface (Advanced Host Controller Interface). And there is SATA drive (or any other device with AHCI interface).
SATA Host Controller (HC) has a number of ports. Theoretically there could be up to 32 SATA ports but not less than 1 (well w/o any port HC itself doesn't make any sense). The number of actual ports depends on implementation. General HC chips used in PC more likely to have 1 or 2 ports. SATA drives are connected to ports. So if SATA HC has 2 ports than up to 2 SATA drives/devices could be attached.
In real life everything is even more interesting. As #Ross Ridge mentioned in comments, port multipliers could be used. Port Multiplier is to increase the number of devices that can be attached. Again port multiplier is device connected to SATA HC port (not to Host Controller itself). One multiplier to one port. Second multiplier could be connected to other port, etc. The support of multipliers is implementation defined. Some HC could work with them, some might not. Multipliers have 16 ports. Port '0xF' is special control port of multiplier. So up to 15 devices could be connected.
So all above is about SATA specification. Considering the listed questions itself:
OS drivers could enumerate and name drives by it's own way. Like you mentioned Secondary IDE Channel or ATA Channel 1. First name more likely is legacy from drives w/ parallel interfaces. In fact the word 'channel' even is not in SATA AHCI specification. There are ports :)
Some fu... drivers could imply "software limitations" like do not support multipliers or work only with one port. Regularly update drivers.
thus providing Windows with a way to change such options like enable/disable DMA mode. Windows DMA mode has nothing to do with SATA drive. SATA Host Controller use special buffers to allocate data received from drives. DMA mode in this case more like how OS get access to these buffers but not how HC communicate with attached drives.
Also can you tell me what is the maximum number of ATA Channels that SATA controller can have?. There are ports. The number of ports is implementation defined. If you know the address of SATA Host Controller on your motherboard read CAP register, 4 low bits are Number of Ports - 1. PS: you will need a driver to get direct access to physical memory so...