How does ETag generated by IIS 7 OR IIS 8

Hi all:

I'm interested in understanding how to generate the Etag by IIS。 For example, the following two values , how to understand，If I convert the value （c7bcbcf940ca1）to the time， I can't get the valid result.

Etag: "c7bcbcf940ca1:0"
Last-Modified: Tue, 29 Sep 2009 11:36:13 GMT

Thank you