how to set heap base and limit

Hi,

I am using keil uVision4 and working on ARM7 processor. I want to know how can we set values for __heap_base and __heap_limit. I have seen these parameters in startup.s file but I could n't find where the definitions have been given. Also what can be the maximum size that we can set for heap. Also I have another question. Its a basic question, please dont mind because Iam new to ARM7 and keil. When I run the code I get the following message in output window

Program Size: Code=3874 RO-data=98 RW-data=12 ZI-data=1292

Code size means size of the code we wrote. That is fine

What does RO-data and ZI-data correspond to and how can we determine what is the maximum RAM that my application needs from the above statement

Thanks in advance