Why does Nvidia video cards have odd memory numbers?

[Dari]

320MB, 896MB, 1790MB. Why these numbers? Also, how come their memory is not GDDR5, but GDDR3?

 

[aka1nas]

The base model card usually has a more traditional number, and they cut down the memory bus and corresponding RAM along with shaders when they make the cheaper models. They were using GDDR3 with a wider bus for the current gen, it may have been a cheaper solution than GDDR5 when the GTX series was released.

 

[Ben90]

Yea GDDR3 was (and still prolly is) much cheaper than GDDR5, GDDR5 has double the theoretical bandwidth of GDDR3 but NVidia decided it was a cheaper solution to double the bus width instead of using more expensive ram, yeilding the same bandwidth at the cost of having a very large die