webpointmorpheus Computer Info
CD & DVD

     Overview      Laser Technology      CD-ROM Formats      DVD      Speeds      W-RW-Read

©2005 - material compiled by Bob Carnaghi, www.webpointmorpheus.com

Overview     Top of Page

In todays computer environment, the floppy drive is considered a relic of the past. It may be hard to believe, but there was a time when the 1.44 MB capacity of the typical floppy disk was a lot of space. As this amount of space shrunk, and the need for more portable storage space became necessary, the CD (Compact Disk) became the unit of choice. Initially designed for music files as a replacement to the antiquated (?) vinyl records, data files were a natural expansion of this medium. A typical CD-ROM disk can hold 650 MB of data. Once again, this technology has been eclipsed by the DVD (Digital Versatile Disk.) The base DVD can hold 4.7 GB of data, see chart below.

Laser Technology     Top of Page

At the heart of the CD and DVD technology is a low powered laser head. This head is capable of writing a series of marks to the disk in a configuration of ones and zeros that can later be read and assembled into information streams. The amazing capacity of data that is available to the DVD is due to layering, see below.

CD-ROM Formats     Top of Page

A CD-ROM disk can come in at least a couple of different formats. A CD-R disk can be written once, and read many times over. A CD-RW disk can be written to many times, ereased and re-formatted, then written to some more. Additionally, the disks can have data or music files added to them if the initial write did not fill up the disk.

The DVD     Top of Page

DVD media was originally designed for an extended storage space to hold movies. As with the music-data progression of the CD, storing data to the DVD was the next logical step in DVD history. DVD's are capable of being SS or DS (Single or Dual Sided) as well as SL or DL (Single Layered or Dual Layered). This can produce an amazing amount of capacity on a single disk, several hours of video, on one disk. See the chart.

Speeds     Top of Page

Speeds of CD and DVD drives are typically stated as a progression of numbers that looks like '12x 8x 32x'. When reading this specification, the first consideration is what the 'x' means. The original specification for CD speed was in terms of 150 KBps. A drive capable of '1x' is capable of a rate of 150 KBps rate. The rate multiplies from there, see the chart.

Write - ReWrite - Read     Top of Page

Once the multiplier is known, the next determination is what is the drive capable of for its operations. This comes down to Write - Rewrite - Read. So for a system that's listed as '8x - 4x - 32x', the system can write data at a rate of 1,200 KBps, ReWrite to the disk at a rate of 600 KBps, and Read data from the disk at a rate of 4,800 KBps.