Media Recognition - Optical Disks part 1

So after covering floppy disks it's on to optical disks.

The three main categories of optical media are Compact Disk (CD), Digital Versatile Disk (DVD) and Blu-ray Disk, although CD also splits into Audio and Data CD. These disks come in two sizes (three for CDs) all with differing capacities, as the table illustrates:

Name	Physical Size (diameter)	Capacity
Standard CD	12 cm	650-870 MB
Standard DVD	12 cm	4.7-17 GB
Standard HD DVD	12 cm	15-60 GB
Standard Blu-ray	12 cm	25-50 GB
Mini-CD	8 cm	185-210 MB
MiniDVD	8 cm	1.4-5.2 GB
MiniHD DVD	8 cm	4.7-18.8 GB
Mini-Blu-ray	8 cm	7.5-15.6 GB
Business Card (CD)	8.5 x 5.4 – 8.6 x 6.4 mm	30-100 MB

Discounting size, all these disks look the same and the only way to visually distinguish them is via labels or other identifying markings. If a disk is blank it cannot be categorised visually, but it can usually be identified by putting it into a DVD-RW drive. Once inserted use the operating system’s file manager to determine the type of disk. For example, in MS Windows XP open ‘My Computer’, right click over the relevant drive and select ‘Properties’. The window that opens up reveals disk type: whether it is an audio CD, data CD, DVD or Blu-ray disk. However, within each disk category there are further distinctions to be made.

Compact Disk (CD)

Compact disks are either audio or data CDs. This is an important distinction to make as it affects how the content is stored on a disk: data files are encapsulated within a file system whereas an audio disk contains tracks and track data.

Both types of CD are available in three sizes. The most common are the standard 12cm diameter disks. Mini-CDs are a scaled down version of standard CDs, being only 8cm in diameter. They were originally developed to hold audio singles but this concept was never commercially successful they are now marketed more towards data holding. Business card disks are rectangular with either square or rounded ends. They are slightly wider than Mini-CDs, but shorter with dimensions ranging from 8.5cm x 5.4cm to 8.6cm x 6.4cm. Due to their small capacity these are often novelty items.

Regardless of whether they are audio or data disks, each size of CD is available in CD-R format and all three sizes of data disk are available as CD-ROM. Standard size CDs also coming in other formats including CD-RW.

Audio and Data CD Comparison

Audio CD:

Type:	Optical storage media
Introduced:	Developed from 1979 and commercially available in 1982
Active:	Yes [2010]
Cessation:	-
Capacity:	Standard CDs hold up to 80 minutes of audio. Mini-CDs can hold up to 24 minutes and business card CDs can hold up to 6 minutes.
Compatibility:	Most computers with a CD drive should be able to read CDs, but older machines may be incompatible with CD-R and CD-RW. Machines without two wells in the loading tray may also be unable to play mini-CDs. CDs can be read in DVD and Blu-ray drives.
Users:	Broad, though declining as the popularity of mp3 players gradually makes audio CDs redundant.

Audio CDs conform to the Red Book standard, also known as IEC 908. This was originally released by Philips and Sony and is one of a set known as the ‘Rainbow Books’ that set out the specifications for all Compact Disk formats. The Red Book includes specifications such as each track lasting a minimum of four seconds.

Data CD:

Type:	Optical storage media
Introduced:	1985
Active:	Yes [2010]
Cessation:	-
Capacity:	Standard CDs hold up to 870 MB of data. Mini-CDs can hold up to 210 MB and business card CDs can hold up to 100 MB.
Compatibility:	Most computers with a CD drive should be able to read CDs, but older machines may be incompatible with CD-R and CD-RW. Machines without two wells in the loading tray may also be unable to play mini-CDs. CDs can be read in DVD and Blu-ray drives.
Users:	Broad. Largely replaced floppy disks for long-term data storage and back up, although the relative cost and risk of damage means that other media, such as USB flash drives are now superseding CDs.

Depending on the specific format of data disks they conform to different standards from the ‘Rainbow Books.’

Recognition

Commercial compact disks are clearly marked as either audio or data CDs. Blank CDs meant for home burning can be used for audio and data files, therefore you cannot determine which a disk is without loading it and examining its content. As mentioned, this is done by loading the disk into a computer’s optical disk drive and using the operating system’s file manager to determine the type of disk. However, the disk format (whether it is CD-R or CD-RW) also needs to be ascertained and this is not revealed by the file manger.