Abstract: A device allowing improved means for protection of magnetic data storage media from over-writing or erasure includes an envelope of such size so as to allow a tight fit of such envelope over the subject storage media and to allow the magnetic data storage media with the protective envelope to slide easily into a device used for reading or writing information from or to the storage media. When the user desires to write information to the storage media, the envelope is removed from the storage media in order to uncover the "write protect notch" on the storage media. If the user desires to protect the storage media against possible erasure or over-writing, the envelope is placed on the storage media so as to cover the write protect notch.