Final answer:
A boot disk needed to restart a computer is known as bootable media, and CDs are an example of such media, read by laser technology similar to barcode scanners.
Step-by-step explanation:
When discussing the situation where a boot disk is needed to restart a computer or device, the boot disk is often referred to as bootable media. These are necessary when the computer's main storage, such as a hard drive or solid-state drive, can't be used to boot the system due to corruption or other issues. Compact discs (CDs), which became popular in the 1990s as audio and data storage devices, are a type of bootable media that are read by a laser interpreting variations in reflections from their surface. This same laser technology is employed in some barcode scanners.