ahcibiosoperating systemssata
What is the relation between AHCI and SATA? How come an OS cannot operate a SATA controller without an AHCI driver, while the BIOS knows how to boot of a SATA hard disk?
What are the difference between the SATA controllers, so that they need a specific AHCI driver?
Does the BIOS has a "driver" inside to operate and boot from a SATA(in AHCI mode) HDD?
This sounds like a BIOS error -- the BIOS isn't finding the right drive to boot from when in AHCI mode. I do not believe you're dealing with an OS issue.
Try stripping the system down to bare minimums.
Plug in only one bootable hard drive (the HDD or SSD, whichever contains the OS system partition) and no optical drives and try booting.
Plug in only one optical drive and no harddrives and try booting. If it doesn't work, disconnect and try the other optical drive.
Plug in only one bootable hard drive and one optical drive. You should be able to boot to the hard drive and the DVD.
When trying to boot from a single device, make sure you try all SATA ports on the motherboard before giving up.
If you can boot in those situations, your problem is the ports you've connected your drives to -- try rearranging them so they connect to different ports, to force the BIOS to enumerate them in the correct order.
If you can boot to the optical drive but not the hard drive, you may have a broken bootloader (eg, if the bootloader is installed to the non-system drive's MBR but not the system drive's MBR). You should be able to fix this from the Win-7 repair console.
If none of those work, make sure you have the latest BIOS firmware and try again. You may need to try resetting the BIOS to defaults and reselecting AHCI mode.
Here are two ways you can determine if it's in AHCI (native) mode.
Open up the Device Manager, click the View menu and select "Devices by connection". Navigate through the device tree, usually the AHCI controller is attached directly to the PCI bus. The controller device should have AHCI in the name and your drive should be attached to it.
Download AS SSD Benchmark, it is small and you don't need to install anything. Intended to benchmark SSD drives, it will also tell you the controller the drive is connected to if you hover over the third line of the device detail (msahci in the pic below).
Best Answer
First of all, the BIOS includes a driver for your on-board AHCI controller. And in case the controller is not on-board but on a PCI card, the card will provide a PCI Option ROM containing a BIOS driver for the controller.
If your firmware supports UEFI, it (or the Option ROM) will also include an UEFI driver for the controller.
The same is true for all other components your PC can boot of (i. e. usually USB, CD-ROM, wired network). Other components usually don't have BIOS/UEFI drivers at all.
Operating systems can use the BIOS or UEFI drivers (for example DOS or Windows 95 do so) but most modern operating systems try to avoid the hassle and work around the limitations of the BIOS drivers and instead use their own driver format.
Common limitations of BIOS drivers:
Which means that during boot, modern OSes will have to repeatedly switch between 16-bit and 32-bit/64-bit single-tasking mode and repeatedly toggle the A20 gate until they have read the OS kernel and at least the disk driver into high memory (640K is usually not enough today); then they will switch to multi-tasking mode and continue loading the rest of the OS using the now loaded kernel and disk driver.
UEFI limitations are less bad (UEFI drivers run in 64-bit mode, but still require single-tasking mode and only one core activated), but still bad enough so that I don't know any OS that tries to use UEFI drivers after boot - and which is probably also the reason nobody wrote a web browser for pure UEFI (web browsers are inherently multi-threaded and it would be hard to write a well-performing single-threaded web-browser).