question about the system limits

[Xiong Zhao]

hello,all.now i'm completely confused with the meaning of 
some system limits on kernel 2.4.3.there are three main 
limits that i concern:NR_OPEN,NR_FILE,and OPEN_MAX.i didn't
find NR_INODE anywhere.is that due to the change of the 
allocation mechanism of inodes?in limits.h of the source file
of kernel 2.4.3,NR_OPEN and OPEN_MAX are 1024 and 256 respectively.
but in fs.h,NR_OPEN is defined to be 1024*1024,and NR_FILE is
8192.what's the meaning of these limits?which will work on the 
whole system?which work towards a single user or process?
besides,what's the relationship between these limits and file
file-max,threads-max under directory /proc?it is refered in many
papers that performance can be improved by resetting these values.
but what's their meaning and how they make effect?can anyone
give me a clear explaination?

regards

james