Timing

• The video card and the monitor both have performance limits, which XFree86 is careful to stay within to avoid damaging the hardware.
• vertical frequency: How often the whole screen is refreshed. Higher frequencies give less flicker; 70 Hz or more best.
• horizontal frequency: How often the monitor scans a scan line.
• dot clock: How often the video card outputs a pixel.
• The horizontal frequency is slightly greater than the product of the vertical frequency and the vertical resolution.
• The dot clock is slightly greater than the product of the horizontal frequency and the horizontal resolution.