---
name: "ahci"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["freebsd", "openbsd"]
url: "https://new.carta.tech/ahci"
---

# ahci(4)

Advanced Host Controller Interface for Serial ATA

## NAME

**ahci** – Advanced Host Controller Interface for Serial ATA

## SYNOPSIS

**ahci\* at acpi?** **ahci\* at fdt?** **ahci\* at pci?** **ahci\* at jmb?**

## DESCRIPTION

The **ahci** driver provides support for Serial ATA controllers conforming to the Advanced Host Controller Interface specification.

Several AHCI capable controllers also provide a compatibility mode that causes them to appear as a traditional ATA controller supported by [pciide(4)](/pciide/4.md).

Although **ahci** controllers are actual ATA controllers, the driver emulates SCSI via a translation layer.

Setting the lowest bit (0x1) of the driver flags forces **ahci** to negotiate SATA 1 (1.5 Gb/s) transfer speeds only. It may be useful where higher speeds are unstable.

## SEE ALSO

[intro(4)](/intro/4.md), [jmb(4)](/jmb/4.md), [pci(4)](/pci/4.md), [pciide(4)](/pciide/4.md), [scsi(4)](/scsi/4.md)

## HISTORY

The **ahci** driver first appeared in OpenBSD 4.1.

## AUTHORS

The **ahci** driver was written by David Gwynne ⟨*dlg@openbsd.org*⟩ and Christopher Pascoe ⟨*pascoe@openbsd.org*⟩.