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If you sit down at your PC and fire up MAME for a quick game of Galaxians,
there's two main reasons why it doesn't look like the original arcade game...
.The monitor is orientated the wrong way
.The monitor has the wrong horizontal scanrate
The first problem's solvable with some PC monitors as you may be able to rotate them
NOTE: it is dangerous to rotate monitors not designed for this purpose.
Or, you can just play horizontal games
As for the second, whatever you do - it's still going to be obvious that you're using the 'wrong' monitor
The only way that the display is going to look 'right', is if you use the right monitor -
the monitor that the game was originally intended to run on.
Understanding Monitor Specs
Horizontal Scanrate
The single most important value when you look at any monitor's specs is the horizontal scanrate
This value will tell you almost everything you need to know about the monitor's capabilities
It governs the length of time it takes to draw a complete horizontal line on the display
By default, it also defines the number of lines that can be drawn within a complete vertical refresh cycle,
and the time needed for a horizontal or vertical retrace
in effect - it tells you the resolution of the monitor
The scanrate will probably be one of the following:-
| Resolution | Scanrate |
| 15.75kHz | |
| 25.00Hz | |
| 31.5kHz |
Other monitor spec values are useful, but only if you know the horizontal scanrate
For instance:-
'640x480 at 60Hz'
on it's own doesn't tell you much about the monitor
- as it could describe anything from a domestic (NTSC) TV to a SVGA PC monitor
Monitor Size
A monitor's dimensions are described with just one value - 19 inch, 25inch, 33inch etc.
This is actually the length of the longest diagonal of the monitor screen
i.e. the distance between the top left hand corner and the bottom right hand corner
This dates back to when CRTs (Cathode Ray Tubes) were circular and their size
was described using the diameter of the circle
Horizontal Resolution
The horizontal resolution is probably the most misleading, as it's thoeritically possible to have just about any
horizontal resolution on any type of monitor
All that happens is that at some point, physics kicks in....
To make an image, the electron guns are scanning across the display horizontally at a fixed speed
(the horizontal scanrate)
The colour content of each 'pixel' displayed is determined by the R,G,B values present for any given moment in time
So, if we setup a high enough 'dot' clock (speed at which pixels are turned on/off), we could pump out just about any horizontal resolution
The two things that stop us from doing that are:
.The pysical speed at which we can turn an electron gun on/off
.The 'dot pitch' of the phosphors on the monitor
For the most part, the second 'limitation' will determine the actual horizontal resolution of the display
but - that's not to say that a higher horizontal resolution can't be displayed on the monitor
it just means that each phosphor (or triad of phosphors for colour monitors)
will be used for more than one 'pixel'
So, on even a low resolution monitor - you could feed in a horizontal resolution of 1000,
the image would still be displayed - but some pixels wouldn't have a unique phospor triad.
Vertical Resolution
This is a more accurate indicator of the limitations of the monitor, but it does have one pitfall - interlacing
Interlacing is a technique which allows you to effectively double a monitors vertical resolution,
and is used by all domestic TV formats
It's a method of drawing an image in two passes, the first draws the odd lines, the second the even
(when referring to TV images, these are often called odd and even 'fields')
So, a low res monitor is perfectly capable of display a 480 line image at 60Hz,
or a 600 line image at 50Hz
