Optical backing storage media such as CDs and DVDs can store large files, with CDs holding files smaller than 1Gb such as music and DVDs holding several Gb such as movies. Both CDs and DVDs are portable and can store computer data. CD-ROMs can store data permanently but cannot delete or edit saved data, while CD-RWs and DVD-RWs allow updating of information by recording over old data. Blu-ray discs have the largest storage capacity of optical media. Solid state storage and memory sticks are more robust forms of removable storage that are smaller and more easily transported than optical discs.