Disks that use optical techniques for recording and replay of material without the read/write heads touching the disk. These offer large storage capacities on ‘CD sized’ 5.25-inch (12 cm) polycarbonate disks with technologies including CD, DVD and Blu-ray Disc. These offer capacities of 700 MB for CD, 4.37- 15.90 GB for DVD and 25-128 GB for Blu-ray Disc. The CD format was designed for audio; DVD was designed for SD video and Blu-ray Disc for HD video. All have another life in data storage. They are all available in ROM and read/write forms. The next development is expected to be a disk able to store a 4K UHD movie, which will also be useful for storing large quantities of data.