---
name: "cpu"
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/cpu/4"
---

# cpu(4)

Central Processing Unit

## NAME

**cpu** – Central Processing Unit

## SYNOPSIS

**cpu0 at mainbus?** **cpu\* at mainbus?**

## DESCRIPTION

Several processor models have additional features that extend their base functionality, such as power and frequency control or thermal monitoring.

The [sysctl(2)](/sysctl/2.md) *hw.cpuspeed* returns the current operating frequency of the processor, though on some processors this value may be only an approximation. If possible, speed may be adjusted by altering *hw.setperf* from 0 to 100, representing percentage of maximum speed.

There are several possible implementations for speed adjustment, all transparent to the user:

- EST

  Enhanced SpeedStep found on Intel and VIA processors, offering frequency scaling with numerous positions.

- PowerNow

  Found on various AMD processors. It currently only supports a limited set of models in the K8 families.

The presence of extended instruction sets can be determined by the sysctl *machdep*:

- xcrypt

  Supports the VIA AES encryption instruction set.

The sysctl *hw.sensors* returns the current temperature reported by the processor.

## SEE ALSO

[sysctl(8)](/sysctl/8.md)

## BUGS

Due to the way in which thermal information is reported on Intel processors, the temperature may be off by exactly +/-15 degrees C.

For multiprocessor kernels with more than one CPU sensor, processors report identical temperatures since the temperature is taken from the processor running the sensors update.