Wow, there are a lot of bad explanations in that thread. A lot of it seems to stem from people not making the distinction between SCSI commands and lower-level transports, many of which also have SCSI in their names. But that seems to be pretty common in storage, where the separation of layers isn't as clear as on the Internet.

This is because SCSI is harder to implement, but SCSI is more flexible, and ATA was not flexible enough to support first CD drives.

So with first "civilian" CD drives, appear few proprietary interfaces and some used sort of SCSI.

Than just made decision, to save resources, make hybrid, using ATA electronics, but partially SCSI logic/software.

> SATA HDDs nor CD drives talk any AHCI.

I bought a used HP EliteDesk Mini G1 off eBay to replace a Raspberry Pi for a project. It requires a SATA m.2 which needs an AHCI controller on-board. Very difficult to find.

> It requires a SATA m.2 which needs an AHCI controller on-board.

That doesn't sound right. AHCI is a software protocol for communication between the operating system and host bus adapters. If it's a M.2 SATA SSD, then the host system needs an AHCI controller or equivalent providing SATA ports (such as a SAS HBA, which provides SATA compatibility but is rarely wired up to a M.2 slot).

Or if it's a M.2 PCIe slot in a system that predates widespread NVMe support, then it needs a PCIe SSD that implements AHCI instead of NVMe, in which case there would be no SATA involved anywhere in the chain—just backwards compatibility with software expecting the usual SATA drive behind AHCI controller combination.

Parent misunderstood the G1 SSD requirements. It supports either PCIe AHCI m.2 (predating NVME) or SATA m.2.