Finally, CD-ROM drives that can write are becoming cheap enough for the average person. These drives can be used to back up an entire hard disk on a CD-ROM instead of tape. One can also use a CD-ROM disk as a kind of volatile storage, just like one would use a hard disk, writing, rewriting and deleting files. The way this works is that the old version of the file is burned out of existence by burning pits into every position, thereby obliterating it. The new version is then written to the free area of the CD-ROM. When the CD-ROM fills up, no more files can be rewritten and the state of the CD-ROM is frozen. However, CD-ROMs are still quite slow compared to hard disks so they are not likely to supplant traditional magnetic disks soon.