This is the most common protection which is used to check if the CD is available or not. It is not really used as a Copy Protection.
File patches are needed as there is no generic tool which removes all possible CD-Checks.
For older games there is a utility called Un-CDCheck. This utility can remove a common CD-Check from about 60% of the older games!
For newer games Game Jackal is a good solution as it supports most commercial copy protections, except for the very latest ones.
No-CD patches remove the CD-Check from a game (or application) so the CD (or backup CD) is not needed in the CD-ROM to play it. Usually additional data needs to be copied from the CD to the installation directory to get it to work.