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The preceding list of available resolutions contains modes of the following 'Types'
Unchained VGA
Unchained 'half y' VGA
SVGA
These have the following meanings
Unchained VGA
For historic reasons, normal VGA modes are confined in size to 64K
This places a severe limit on the resolutions that are available to you, however it's possible to split up
or 'unchain' the VGA video memory so that it has access to 4 64K 'planes'
This means you can now access 256K of memory, allowing far more resolutions
It's not quite that simple - as there's still only 64K of memory 'mapped' to PC memory at any one time
which means blitting in these modes is slighty more complex than it is in normal VGA modes.
The advantage of having 4 times the memory generally out weighs the extra programming overhead though
i.e. they are all 256 colour modes
Unchained 'half y' VGA
These are identical to the unchained VGA modes except they can be used to 'fake' medium-res
on a standard/lowres arcade monitor
The 2 modes (512x448 and 512x512) could not be displayed on an arcade monitor without interlacing,
the 'y' resolution is simply too high.
To get round this, the 2 modes only display every other horizontal display line
- but keep the correct aspect ratio
The produces a very stable picture and ,on medium-res raster games, the effect is fairly convincing.
Again, these 2 modes are 8bit modes(256 colours)
SVGA
The 640x480 SVGA mode is just that -
a normal SVGA mode reprogrammed to run on an arcade monitor
It's slighty complicated by the fact that there is no SVGA register set standard,
so drivers would have to be written for each SVGA chipset in order for it to work on all cards
At the moment, there are 2 SVGA drivers in MAME -
ATI
'generic'
For a detailed discussion about the SVGA arcade monitor mode see the next few pages
Using MAME's SVGA Arcade Monitor Mode
The SVGA mode supports both 8bit and 16bit colour depth
