Video RAM on older cards

Everytime I check out an older video card, the "Basic Display RAM Size" seems to be 256K, while the "Texture Memory" can be 512K or 1MB.  I'm trying to define these two terms for memory, and relate them to the total memory in a video card.  Most of the cards I'm looking at are from the early 90's or late 80's.

Anybody know where I can find out more information, or care to comment?

What is "Texture Memory" vs. "Basic Display RAM Size" vs. "RAM" on the video card?