This article explains why a Macintosh LC 475 with 1,024K of VRAM support the 832 x 624 screen size at thousands of colors, but the LC 630 cannot support thousands of colors at 800 x 600.

The video memory for the Macintosh 630 series is split into two sections. The first section holds the graphics data -- the standard display that is generated by the computer. The second section holds the video data from the video input module.

The second section uses 300K of video memory for gathering video-in images. This leaves 724K of video memory available for displaying the standard graphics screen. There is no way to use the 300K of video memory from the second section for displaying 16-bit color at screen sizes larger than 64 0x 480.