Increasing archive list of entries to more than main page list of entries

Hi all,

In my blog options (under ‘reading’ sub tab) I have specified 5 posts on my main page, but if you click on the archives or category archives, they also only list 5 posts. What I would like to do is keep the 5 post limit on the main page but increase the archive list of entries to say, more than 20.

Can anyone tell me which page I need to edit to achieve this? Can’t seem to find the code that does that…

Thanks always for your time and effort, much appreciated.