Old MS-DOS & WIN Software

On 12/7/2005 at 10:11 AM Gil Carrick wrote: True, but that doesn't address where the video ROM image in NTVDM comes from. I believe it's merely a mapped in RAM copy of the ROM. To do otherwise would likely involve taking a speed hit whenever a routine inside a 16-bit NTVDM session accessed the video ROM space, which seems unlikely. Still, it'd be easy enough to check--just put a probe on the CS pin of the video rom and see what happens when a 16-bit app accesses the memory area. BTW, this little topic is a bone of contention for some. There's a group who insist that enabling the BIOS option "Cache Video ROM" is necessary for maximum performance under Win 2K and XP. Perhaps during early startup, but once the generic VGA driver's loaded that's all water under the bridge--and caching is wasted physical memory. What's really water under the bridge is 16-bit mode in Windows. Vista doesn't support it, period. Maybe someone will write a 16-bit emulator for Vista and we'll get to keep our old apps in some form. I can understand MS wanting to deprecate a lot of the PC legacy features. NT startup has to be one of the more complex computing tasks around and I suspect that the folks in Redmond have envied Apple for a long time in not having to accomodate all sorts of bizarre departures from the norm in hardware. All of which has me wondering how much longer things like 8237-type-DMA will be part of the PC platform. Cheers, Chuck