CD-ROM drives and disks can store a lot of information in a small physical space. This is one of the advantages they have over magnetic hard disks and drives. However, they access the information at a slower rate. That is why you will spend more time waiting for programs or files to load if you are launching or opening them from a CD-ROM drive.
When you operate your CD-ROM drive, a laser beam actually looks for the information that is located on your spinning CD disk. The amount of time it takes the laser beam to move to the disk sector containing the specific information is called seek time. Today, 600 milliseconds is considered an average seek time.
After the laser beam has found the data it was looking for, this information still has to be transferred to your CPU or hard drive before you can interact with it. The rate at which your CD-ROM drive reads the data and copies it to your CPU or hard drive is called the Data Transfer Rate. This rate is measured in KB (kilobytes per second) Early CD-ROM drives had a Data Transfer Rate of 150 KB per second. The MPC Level 2 Specification calls for a Data Transfer Rate of 300 KB per second. These faster drives are called double speed drives. Faster and faster drives are continually being introduced in the market, at more affordable prices. If you purchase a CD-ROM drive today, you will have a variety of triple speed and even quad speed drives to choose from.
CD ROM FORMATS - INTRO AND BRIEF DESCRIPTION W/CDI
The same type of disk that is used for audio CDs is also used for multimedia applications. The difference between the disks is the way that they are formatted.
The Red Book standard format is used for all audio CDs today. This standard evolved into the Yellow Book standard, which was the first computer CD-ROM disk. You can play audio CDs in your computer CD-ROM drive because the audio CD standard was developed first. Unfortunately, not all formats are as compatible. Several formats found in the market today are proprietary or platform specific. For example, the CD-I (CD Interactive disk format developed by Phillips can only be played in a CD-I player manufactured by Phillips. The MAC HFS disk was developed from the Yellow Book standard, but it can only be used in Macintosh systems.
However, there is a trend towards compatibility . Any CD-ROM drive can read a disk with High Sierra format, provided that the data on the disk is also in a universal format such as ASCII text. And the ISO (International Standards Organization) 9600 format allows a CD-ROM reader to interpret data as long as you have a driver on your system that translates the data format for you.
Multisession-compatibility
Most CD-ROM disks are recorded form start to finish in one session. All the data has to be prepared in advance. Once the recording has begun, it cannot be interrupted. For certain applications, it is desirable to record the CD data in pieces, starting and stopping several times. A CD-ROM drive which can read disks that were recorded in more than one session are called multisession -compatible drives. The most common uses of multisession capabilities today are Photo-CDs. This type of application is used to record photographs that are viewed on your computer.
CD-ROM XA
The "XA" in CD-ROM XA stands for "extended architecture. " This feature allows audio data and video data meant to be played back synchronously to be written to the same physical disk sector. This allows your CD-ROM drive to access the information much more quickly than if the audio track file and the video track file were located in different physical disk sectors.
