Even back then there was already a large gap widening between the slowest and fastest graphics cards. Between the bus widening from 8-bit > 16/32-bit, graphics

Even back then there was already a large gap widening between the slowest and fastest graphics cards. Between the bus widening from 8-bit > 16/32-bit, graphics cards supporting posted writes so the CPU wouldn't have to wait as much, and faster CPUs, fast systems could write a 640x480x256 screen at 300 fps or faster. In your case, you may have even either had a cached system memory buffer and DMA copy, or the drawing being done by a blitter. But even in the time of Win98, some 3D cards on the low end had really slow CPU access that barely beat an old ISA bus card. Screen resolutions have gotten so high that there's a bit of a reversal again -- even if you can redraw an entire 4K screen at 60 fps, it's not exactly efficient. Games typically still redraw everything, but desktop compositors definitely do some optimizations, including dynamically assigning layers to hardware planes to reduce redrawn area.