Media Recognition - Optical Disks part 2

CD-ROM

Type:	Optical storage media
Introduced:	1985
Active:	Yes [2010]
Cessation:	-
Capacity:	Size dependent. Standard data disks have a maximum capacity of 870 MB and audio disks can hold up to 80 minutes of audio.
Compatibility:	All drive developments should be backwards compatible and therefore be able to read any CD-ROM.
Users:	Use for commercial music, but declining. Used to hold software – games etc.
File Systems:	ISO9660, HSF, UDF, HFS/+, Red Book Audio

Recognition

CD-ROM stands for Compact Disk-Read Only Memory and is a manufactured pre-pressed disk. As a data disk it is commonly used to hold and distribute software and as an audio disk it contains commercial music. Because these are predominately commercial disks they are not the most common form of CD to be found in an archive collection, but it is not unheard of.

Because these disks are manufactured and made commercially available they are usually very easy to identify: it is unusual to find a completely blank CD-ROM. These disks conform to the Yellow Book standard if containing data, or Red Book if they are audio disks.

CD-R

Type:	Optical storage media
Introduced:	1990
Active:	Yes [2010]
Cessation:	-
Capacity:	Size dependent, but standard CD-R holds a maximum of 700MB of data or 80 minutes of audio track
Compatibility:	Pre-1990 machines may be incompatible with CD-R formatted disks but all other optical drive types should be able to read them.
Users:	Broad but declining. Preferred over CD-RW for long term preservation due to longer lifespan, but being superseded by more reliable, larger capacity data storage devices.
File Systems:	ISO9660, UDF, HFS/+, Red Book Audio
Common Manufacturers:	Maxell, Philips, Sony, Verbatim, Memorex

Recognition

CD-R stands for CD-Recordable and is also known as CD-WO (CD-Write Once). These disks can be written to once and the data or audio added cannot be erased or written over. However, the data does not have to be added all at once; provided there is free space on the disk, more data can be added at a later date. This is multisession recording.

Data CD-R disks adhere to the Orange Book standard and audio CD-R disks conform to the Red Book standard.

Most CD-R disks are clearly labelled as such, though they can be blank. If this is the case more detail can be obtained from the report produced by imaging software during the disk image process. The report often states what type of CD the disk is, although in a few cases it does not.

CD-RW

Type:	Optical storage media
Introduced:	1997
Active:	Yes [2010]
Cessation:	-
Capacity:	Size dependent, but standard size CD-RW holds a maximum of 700 MB of data or 80 minutes of audio track.
Compatibility:	Pre-1997 machines may be incompatible with CD-R formatted disks but all other optical drive types should be able to read them.
Users:	Broad but declining. To large extent replaced floppy disks for short 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 CD-RW.
File Systems:	ISO9660, UDF, HFS/+, Red Book Audio
Common Manufacturers:	Maxell, Philips, Sony, Verbatim, Memorex

Recognition

CD-RW stands for CD-Rewritable. These disks can be written to, with the data then being deleted and new data written to the disk. Such a disk typically has around 1,000 write cycles. As with CD-R the book standard is orange for data disks and red for audio.

The disk format is also determined in the same way as CD-R: through the disk image report if the disk itself is devoid or labels or markings.