I work on legacy systems and I used to see revision history of files or functions being modified every release in the source code, for example:

//
// Rev. No     Date      Author   Description
// -------------------------------------------------------
//   1.0    2009/12/01   johnc    <Some description>
//   1.1    2009/12/24   daveb    <Some description>
// -------------------------------------------------------
void Logger::initialize()
{

    // a = b;             // Old code, just commented and not deleted
    a = b + c;            // New code

}

I'm just wondering if this way of documenting history is still being practiced by many today? If yes, how do you apply modifications on the source code - do you comment it or delete it completely?

If not, what's the best way to document these revisions? If you use version control systems, does it follow that your source files contain pure source codes, except for comments when necessary (no revision history for each function, etc.)?