MGMT 1050 Lecture Notes - Lecture 28: Constant Linear Velocity, Portable Cd Player, Reaction Rate Constant
MGMT 1050 Lecture 28 Notes – Magnetic Files
Introduction
• The blocks can be arranged in files, with a directory structure similar to that of magnetic
disks.
• The technical details are very different, however.
• The layout of a CD-ROM to that of a sectored magnetic disk.
• Rather than concentric tracks, data on a CD-ROM is stored on a single track,
approximately three miles long, which spirals from the inside of the disk to the outside.
• Instead of sectors, the data is stored in linear blocks along the track.
• It should be remembered that the CD design was originally intended primarily for audio
applications, where most data access is sequential, from the start of a musical selection
to its finish
• Thus, a single spiral track was a reasonable decision.
• Since the CD format was designed for maximum capacity, the decision was made to
pack the bits on the disk as tightly as possible.
• By making each blocks the same length along the spiral track, regardless of location on
the disk.
• Thus, the disk is read at a constant linear velocity (i.e., CLV), using a variable speed
motor to keep the transfer rate constant.
• Since the angle of a block is smaller on the outer tracks, the disk moves more slowly
when outside tracks are being read.
• This is easily observable if you have access to a portable CD player that allows you to
observe the disk as it rotates.
• A CD-ROM typically stores 270,000 blocks of data.
• Each block is 2352 bytes long and holds 2048 bytes of data.
• In addition, there is a 16-byte header, which provides 12 bytes to locate the start of a
block and 4 bytes for block identification.
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