Cathode ray tubes
A high speed exposure shows an electron beam in the process of scanning an image
In a CRT, the scan rate is controlled by the vertical blanking signal generated by the video controller, ordering the monitor to position the beam at the upper left corner of the raster, ready to paint another frame. It is limited by the monitor's maximum horizontal scan rate and the resolution, since higher resolution means more scan lines.
The refresh rate can be calculated from the horizontal scan rate by dividing the scanning frequency by the number of horizontal lines multiplied by 1.05 (since about 5% of the time it takes to scan the screen is spent moving the electron beam back to the top). For instance, a monitor with a horizontal scanning frequency of 96 kHz at a resolution of 1280 × 1024 results in a refresh rate of 96,000 / (1024 × 1.05) ≈ 89 Hz (rounded down).
Liquid crystal displays
Much of the discussion of refresh rate does not apply to the liquid crystal portion of an LCD monitor. This is because while a CRT monitor uses the same mechanism for both illumination and imaging, LCDs employ a separate backlight to illuminate the image being portrayed by the LCD's liquid crystal shutters. The shutters themselves do not have a "refresh rate" as such due to the fact that they always stay at whatever opacity they were last instructed to continuously, and do not become more or less transparent until instructed to produce a different opacity. Most of the TFT LCDs used in portable devices and computer monitors need a continuous refresh. The driving voltage determines the transmittance of the liquid crystal.
Computer displays
On smaller CRT monitors (up to about 15"), few people notice any discomfort below 60–72 Hz. On larger CRT monitors (17" or larger), most people experience mild discomfort unless the refresh is set to 72 Hz or higher. A rate of 100 Hz is comfortable at almost any size. However, this does not apply to LCD monitors. The closest equivalent to a refresh rate on an LCD monitor is its frame rate, which is often locked at 60 fps. But this is rarely a problem, because the only part of an LCD monitor that could produce CRT-like flicker—its backlight—typically operates at around 200 Hz.
Different operating systems set the default refresh rate differently. Microsoft Windows 95 and Windows 98 (First and Second Editions) set the refresh rate to the highest rate that they believe the display supports. Windows NT-based operating systems, such as Windows 2000 and its descendants Windows XP, Windows Vista and Windows 7, set the default refresh rate to a "conservative" rate, usually 60 Hz. The many variations of Linux usually set a refresh rate chosen by the user during setup of the display manager (although a default option is usually included with xfree86). Some full-screen applications, including some games, allow the user to reconfigure the refresh rate before entering full-screen mode, but most default to a "conservative" resolution and refresh rate and let you increase the settings in the options.[citation needed]
Old monitors could be damaged if a user set the video card to a refresh rate higher than the highest rate supported by the monitor. Some models of monitors display a notice that the video signal uses an unsupported refresh rate.
Stereo displays
When LCD shutter glasses are used for stereo 3D displays, the effective refresh rate is halved, because each eye needs a separate picture. For this reason, it is usually recommended to use a display capable of at least 120 Hz, but 200 Hz is optimal. Unfortunately most monitors cannot handle this rate, especially at higher resolutions.
Decided I needed a new screen today and went to Computer Corporation. 
There must be a logical reason.
