Service & Catalog on C:\pub\Catalog.wci

Hi,
On all my NT Servers running IIS 4.0, in Event Viewer, I get this..
1. “CI Service Started successfully !!” &
2. “Catalog done on C:\Inetpub\Catalog.wci”

What is the Catalog.wci folder in Inetpub ? I see lots of files there like CI~.001. What are they ??
Akash