Which best describes an optical disk?

An optical disk is best described as an electronic storage device for data. This is because optical disks, such as CDs, DVDs, and Blu-ray discs, utilize laser technology to read and write data. The information is encoded on the disk in the form of tiny pits and lands that reflect light differently when read by a laser. This method allows for significant amounts of data to be stored in a compact format.

The other options do not accurately represent what an optical disk is. A printed circuit board, for instance, is primarily used to connect electronic components and does not store data in the same manner as an optical disk. RAM (Random Access Memory) is a type of volatile memory used for temporary storage while a computer is running, rather than for long-term data storage like that of an optical disk. Lastly, while mainframe systems may use various storage components, describing an optical disk as a component of mainframe systems is misleading; optical disks can be utilized across many computing platforms and are not limited to mainframe usage.