cytune

cytune [-I] [-s] [-r] [-f]

-I
    Display detailed CPU information and current configuration register values.


-s
    Enter interactive mode to set CPU multiplier and other parameters.


-r
    Reset configuration registers to factory defaults.


-f
    Force operation, bypassing some safety checks (use with extreme caution).

cytune is a utility designed to configure and tune Cyrix 6x86, 6x86MX, and M II processors by accessing their internal configuration registers via I/O ports. It allows users to adjust critical settings such as the CPU clock multiplier, write allocate buffer, branch target buffer, and other performance-related features.

Running cytune without options launches an interactive menu displaying current settings and options to modify them. This tool was essential in the 1990s for optimizing Cyrix CPUs, which had unique configuration capabilities not exposed through standard BIOS. Improper use can cause system instability or permanent CPU damage, so backups and caution are advised.

Primarily used on older x86 systems, cytune reads/writes specific I/O ports (e.g., 0x22, 0x23 for CCR) to enable features like 3x multiplier lock or suspend mode. It performs CPU detection to ensure compatibility.

Risk of CPU damage or system lockup if misused; requires root privileges; incompatible with modern CPUs; test settings incrementally.

Always run as root. Verify CPU model first with cat /proc/cpuinfo. Incorrect multiplier can overclock/underclock lethally.

Default mode shows menu: select options like 'M' for multiplier, 'W' for write allocate. Save with 'S', quit with 'Q'.

Developed in the mid-1990s by Stefan Reinauer for Cyrix 6x86 CPUs. Included in early Linux distributions' utils; largely obsolete since Cyrix acquisition by VIA and shift to AMD/Intel dominance.

cpuid(1), setserial(8), hdparm(8)