Looks like

Subject: Looks like
Name: ludicrous
Date: 3/8/2001 1:46:02 AM (GMT-7)
IP Address: 138.67.74.229
In Reply to: Nvidia GeForce2 MX200 and MX400 - enlighten me posted by Sledge
Message:

they've differentiated the chip by memory support now, the MX 200 only supports 64-bit SDRAM and the MX 400 only supports 128-bit SDRAM and DDR...that way OEMs looking for the lowest-cost solution can pay less and buy the MX 200 part.

Check out Tony Smith's bit at The Reg