From Wikipedia:
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• Multicolor mode: 64×48 pixels (each pixel may be any color, all 32 sprites are available)
• Bitmap mode: 256×192 pixels (no more than two colors in an eight pixel row, full 15 color palette + transparent, all 32 sprites available)
• Graphics mode: 32×24 characters (256 8×8 user-definable characters, full 15 color palette + transparent and 32 sprites.
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The last was the mode accessible from Basic and Extended Basic. I remember longing for the bitmap and multicolor mode.
For the 256x182 mode, the pixel bitmap is 5824 bytes bitmap, plus 1 byte for color info of each 8-pixel (4-bit foreground/4-bit background) which is also 5824 bytes. Total 11648 bytes. Just 2 bits per pixel BTW.
The TI994a had 32 sprites (all single colored 8x8 pixels). You could also magnify them.
Also from Wikipedia:
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The TMS9918 was the basis for the VDP chips in the Sega Master System, Game Gear and Mega Drive. They used additional display modes and registers, and added hardware scrolling capabilities and other advanced features. (Note that the Mega Drive VDP cannot access any of the TMS9918 display modes discussed below.)
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