The Hitchhiker's Guide to X386/XFree86 Video Timing
or, Tweaking your Monitor for Fun and Profit

Eric S. Raymond This e-mail address is being protected from spam bots, you need JavaScript enabled to view it

This is version 1.0, Jan 8th 1993.

1. Introduction

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The XFree86 server allows users to configure their video subsystem and thus encourages best use of existing hardware. This tutorial is intended to help you learn how to generate your own timing numbers to make optimum use of your video card and monitor.

We'll present a method for getting something that works, and then show you how you can experiment starting from that base to develop settings that optimize for your taste.

f you already have a mode that almost works (in particular, if one of predefined VESA modes gives you a stable display but one that's displaced right or left, or too small, or too large) you can go straight to the section on Fixing Problems. This will enlighten you on ways to tweak the timing numbers to achieve particular effects.

Free86 allows you to hot-key between different modes defined in XF86Config (see XF86Config.man for details). Use this capability to save yourself hassles! When you want to test a new mode, give it a unique mode label and add it to the end your hot-key list. Leave a known-good mode as the default to fall back on if the test mode doesn't work. The Xconfig section at the end of the second Example Calculation provides a good example of how to record your experiments in a way that will help you quickly converge on a solution.

First check out the Monitors file in lib/X11/doc If your monitor is in it, you can probably skip the rest of this document! You may need to scale some of the timing numbers if the clock used to generate the mode in the database doesn't match what your card has available, but that's easy.