5.3Non-von Neumann Architectures131Let’s look for a moment at the acronym CD. CD, of course, stands forcompact disk—you probably have a collection of them with recorded music.A CD drive uses a laser to read information stored optically on a plasticdisk. Rather than having concentric tracks, there is one track that spiralsfrom the inside out. Like other disks, the track is broken into sectors. Unlikemagnetic disks where the tracks near the center are more densely packed, aCD has the data evenly packed over the whole disk, thus more informationis stored in the track on the outer edges and read in a single revolution. Inorder to make the transfer rate consistent throughout the disk, the rotationspeed varies depending on the position of the laser beam.The other letters attached to CD refer to variousproperties of the disk, such as formatting, and whetheror not the information on them can be changed. CD-DAis the format used in audio recordings: CD-DA standsforCompactDisk-DigitalAudio. Certain fields in the
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Computer data storage, Read-only memory, Acronym and initialism, CD-ROM, Non-von Neumann Architectures