ICT 0417 - Topic 3: Storage Devices and Media

Optical Drives: CD, DVD, Blu-ray

Optical drives are storage devices that read and write data using lasers. They work by shining a laser beam onto a disc and detecting the reflected light. The pattern of reflected light represents the data, which is then translated into digital information.

Types of Optical Drives

There are several types of optical drives, each with different storage capacities and capabilities:

• CD-ROM (Compact Disc Read-Only Memory): These are read-only discs, meaning data is pre-recorded on them during manufacturing. They typically store up to 700MB of data.
• CD-R (Compact Disc Recordable): These discs can be written to once. They use a dye layer that changes color when exposed to a laser. They also store up to 700MB of data.
• CD-RW (Compact Disc ReWritable): These discs can be written to, erased, and rewritten multiple times. They use a phase-change material that can switch between reflective and non-reflective states with a laser. They also store up to 700MB of data.
• DVD-ROM (Digital Versatile Disc Read-Only Memory): Similar to CD-ROM, but with a higher storage capacity. Single-layer DVDs hold 4.7GB, while dual-layer DVDs hold 8.5GB.
• DVD-R (Digital Versatile Disc Recordable): Similar to CD-R, but with higher storage capacity. Single-layer DVD-Rs hold 4.7GB and dual-layer DVD-Rs hold 8.5GB.
• DVD-RW (Digital Versatile Disc ReWritable): Similar to CD-RW, but with higher storage capacity. Single-layer DVD-RWs hold 4.7GB and dual-layer DVD-RWs hold 8.5GB.
• Blu-ray Disc (BD): These offer significantly higher storage capacities than DVDs. Single-layer Blu-ray discs hold 25GB, while dual-layer discs hold 50GB. Triple-layer discs can hold 100GB. Blu-ray is commonly used for high-definition video.

How Optical Drives Work

1. The optical drive contains a laser diode that emits a laser beam.
2. The laser beam is focused onto the surface of the disc.
3. The laser beam reflects off the disc's surface.
4. The reflected light is detected by a sensor in the drive.
5. The sensor converts the reflected light into electrical signals, which are then interpreted as data.
6. For writing data (CD-R, CD-RW, DVD-R, DVD-RW, Blu-ray), a more powerful laser is used to change the physical properties of the disc's surface.

Comparison Table

Drive Type	Storage Capacity	Read/Write	Typical Use
CD-ROM	700MB	Read-Only	Software distribution, music
CD-R	700MB	Recordable (Once)	Data archiving, burning music CDs
CD-RW	700MB	Re-recordable (Multiple times)	Data archiving, flexible media
DVD-ROM	4.7GB (Single-layer), 8.5GB (Dual-layer)	Read-Only	Movies, software, large data storage
DVD-R	4.7GB (Single-layer), 8.5GB (Dual-layer)	Recordable (Once)	Data archiving, burning DVDs
DVD-RW	4.7GB (Single-layer), 8.5GB (Dual-layer)	Re-recordable (Multiple times)	Data archiving, flexible media
Blu-ray Disc	25GB (Single-layer), 50GB (Dual-layer), 100GB (Triple-layer)	Read-Only/Recordable	High-definition video, large data storage

Note: The actual storage capacity can vary slightly depending on the manufacturer and the specific disc format.

Advantages and Disadvantages

Advantages:

• Relatively inexpensive.
• Portable and easy to store.
• Suitable for archiving data.

Disadvantages:

• Limited storage capacity compared to modern storage devices.
• Can be scratched or damaged.
• Slower data access speeds compared to hard drives or SSDs.