dionb wrote on 2021-11-25, 22:31:
Makes it even weirder - and me blind. I have one and never noticed, just went with Miro's "3MB" promise.
That's actually fair advertising. The usable video memory in that card is either 1MB (in VGA compatible modes) or 3MB (in 24bpp modes). You don't get any mode where all the 3.25 MB are used at once. Just for reference, neither the 16S (I have one) nor the 32S have incomplete banks as the 24S does. The 16S has two banks of 1MB each and the 32S has four banks of 1MB each.
You need an even number of banks, because in high-color modes (and the high-performance 256 color modes), the MiroCrystal 16/24/32S design requires the use of bank interleaving. A card with three banks of 1MB wouldn't work.
The 24S likely performs less than stellar in 16 bit modes (if it supports them at all), because you can only use 16 bit per bank, which is one pixel per memory cycle, as in true color modes. The 16S and 32S can pack two 16-bit pixels into a single memory word (due to the bank width of 32 bits), enabling them to run at higher clocks and use the full RAM. On the 24S, I don't see a way to implement 16bpp without having 16 bits unused in framebuffer space after each 16-bit pixel, so good luck finding software supporting this scheme...
You likely can use the acellerator in one-pixel-per word 16bpp modes if you configure it for true color operation. You just need to set appropriate color values while drawing. Again, performance will suffer compared to two-pixels-per-word. Net effect: For 16bpp, the 2*1MB memory on the 16S is far superior to the 4*0.75MB of the 24S. Don't buy the 24S if you care about 16bpp modes. It's the wrong tool for that job.