Some SVGAs do memory interleaving and other weird stuff.
They require memory expansion to properly work in higher resolution/colour depths.
I've seen this with Windows 3.1 graphics drivers:
Some resolutions/colors depths are available twice.
One is higher performance, but needs a higher memory expansion.
Personally, I really think that piggybacking is worth a try.
I often thought about doing that myself with an old Paradise card..
But be careful, there are two meanings of the piggyback method.
a) Stacking RAMs atop, but with the address lines (RAS, CAS etc) re-routed to be in series.
That way, the RAM logically appears same as if being installed properly in an empty expansion socket.
b) Just stacking RAMs; it's being used for troubleshooting faulty RAM. Both RAMs are working in parallel, no increase in memory.
Edit: If the VGA BIOS is the culprit, it's also possible to use a RAM BIOS version of it:
It's a TSR version of a BIOS that can be loaded in DOS. It installs like a mouse driver or like the VESA VBE TSR and can be found on the VGA card's utility/driver diskette.
The neat thing is that this VGA BIOS *can* be different to what's burned into the. ROM chip on your VGA card.
So ideally, for upgrading your VGA card firmware you don't need to resort to use an EPROM programmer and a blank EPROM.
For testing, that utility might be fine enough. It wastes some memory, of course. 33KB or so.
But that depends on the way the TSR works.
If it's big (24 to 32KB or 48KB) it will contain the whole VGA BIOS.
Otherwise, it's just an utility that copies the ROM version to RAM, for increased performance.
That's what the RAMBIOS was being made for originally, after all.
To not have to call the VGA ROM code over 8-Bit or 16-Bit bus each time.
Edit: But personally, I'd just make sure the VGA card isn't the culprit.
- Are other Genoa users have same problem?
- Are 512KB really required for 800x600 16c on this Genoa model?
Most (S)VGA cards support that mode, even with 256KB. It's the most popular SVGA mode. It was the very reason for VESA VBE to exist.
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