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

# wd(4)

WD100x compatible hard disk driver

## NAME

**wd** – WD100x compatible hard disk driver

## SYNOPSIS

**wd\* at wdc? flags 0x0000** **wd\* at pciide? flags 0x0000**

## DESCRIPTION

The **wd** driver supports hard disks which emulate the Western Digital WD100x. This includes standard MFM, RLL, ESDI, IDE, and EIDE drives, as well as Serial ATA drives, and PCMCIA/CF storage media.

The **flags** are used only with controllers that support DMA operations and mode settings (like some [pciide(4)](/pciide/4.md) controllers). The lowest order (rightmost) nibble of the **flags** define the PIO mode to use. The next four bits indicate the DMA mode and the third nibble the UltraDMA mode.

For each set of four bits, the 3 lower bits define the mode to use and the last bit must be set to 1 for this setting to be used. For DMA and UltraDMA, 0xf (1111) means “disable”. For example, a **flags** value of 0x0fac (1111 1010 1100) means“ use PIO mode 4, DMA mode 2, disable UltraDMA”. The special setting 0x0000 means “use whatever the drive claims to support”.

## SEE ALSO

[intro(4)](/intro/4.md), [pciide(4)](/pciide/4.md), [scsi(4)](/scsi/4.md), [wdc(4)](/wdc/4.md), [disklabel(5)](/disklabel/5.md), [atactl(8)](/atactl/8.md), [disklabel(8)](/disklabel/8.md), [fdisk(8)](/fdisk/8.md)