[ixp1200] what is the difference between IXP1200 Revision C0 and the olders

Hi, The README of "inux 2.4.18 for ixp1200" says that it can not run on silicon older then Rev C0 IXP1200. But, what is the difference between the Rev C0 and the olders? And where can I find the detailed documents about this? Thanks a lot! 　　　　　　　　Li Weihua 　　　　　　　　liweihua@cosix.com.cn 　　　　　　　　　　2002-11-25