Before revision: Both Gregg's and Russell's disc are floppy media read in transparent mode, which imposes serious drawbacks .
After revision: , after this were developed four generations of optical drive that includes Laserdisc (1969), WORM (1979), Compact Discs (1984), DVD (1995), Blueray (2005), HD-DVD (2006), more formats are currently under developementBoth Gregg's and Russell's disc are floppy media read in transparent mode, which imposes serious drawbacks .