Tag Archives: optical media

Media Recognition – Optical Disks part 3

20th century, 21st century, Digital archives, Modern, , , , ,

DVD

 

Type:

Optical storage media

Introduced:

1995

Active:

Yes [2010]

Cessation:

–

Capacity:

1.4-17 GB (although 17 GB disk is very rare. Common large capacity is 9.4 GB)

Compatibility:

DVDs come in two formats: DVD- and DVD+ and neither are universally compatible with disk drives. Some DVD players will only read the same format disks, though DVD writers that only write DVD+R/RW disks will read DVD-R disks. Dual format drives are available which are compatible with both formats.

Users:

Broad. Its larger capacity means it is often favoured over CDs for large data file storage. It is also the medium of choice for watching audio visual material, having superseded VHS video cassettes.

File Systems:

UDF, ISO9660, HFS/+

Common Manufacturers:

Maxell, Philips, Sony, Verbatim, Memorex

 

Recognition

 

DVDs come in two sizes: standard 12cm and 8cm ‘mini-DVD’. As with CDs, these are often clearly marked with the manufacturer and disk type. However, unlike CDs if you put a DVD into a computer disk drive and select ‘Properties’ the window that opens will state not only that it is a DVD, but will also identify the DVD type (i.e. DVD-RW).

The capacity of a DVD varies quite widely and this is due to its construction. Similar to floppy disks, DVDs can be either single or double sided (SS or DS) and can also be single or double layered (SL or DL). This information is not recorded on a disk, but the disk capacity which is shown does suggest how the disk is constructed. The table below shows the different capacities for a standard sized CD. Be aware that DS DL disks are very rare.

Construction

Capacity
Single Sided and Single Layered (SS SL)

4.7 KB
Single Sided and Double Layered (SS DL)

8.5 KB
Double Sided and Single Layered (DS SL)

9.4 KB
Double Sided and Double Layered (DS DL) 17 KB

The capacities for miniDVDs are:

Construction

Capacity
Single Sided and Single Layered (SS SL)

1.46 KB
Single Sided and Double Layered (SS DL)

2.66 KB
Double Sided and Single Layered (DS SL)

2.92 KB
Double Sided and Double Layered (DS DL) 5.32 KB

DVDs also vary in writing speed. Original DVDs were 1x, which means they wrote 1,318 KB/s. This translates to 61 minutes for single layered DVDs and 107 minutes for dual layer. Currently DVD speeds increase by multiples of two up to 24x, with the omission of 14x. There is also 2.4x and 2.6x and speeds available depend on the DVD format. These variations affect writing speed and do not impact on any other aspect of a DVD.

Unlike compact disks, there is no single standardised recordable format for DVDs. Instead two formats are competing for the greater market share: DVD- and DVD+. There is little difference between the two in terms of manufacture and performance. The biggest issue is compatibility as not all DVD- disks work with DVD+ drives and vice versa. In July 2003 the hardware website cdrinfo.com produced a comprehensive compatibility test for the different DVD recording formats which concluded that DVD- is the most compatible (compatible with 92.21% of DVD players and drives). A full list of results, including compatibility results for individual DVD players can be found on the website http://www.cdrinfo.com/Sections/DVDMediaFormats/

DVD Formats

This table lists the different DVD formats and the years they were introduced. DL stands for Double Layer.

Format

Year Introduced

Features
DVD-R 1997 Write once media
DVD+RW 1997 Rewriteable media
DVD-RW 1999 Rewriteable media
DVD+R 2002 Write once media
DVD+R DL 2003 Write once, dual layer media
DVD-R DL 2005 Write once, dual layer media
DVD+RW DL 2006 Rewriteable, dual layer media
DVD-RW DL 2007 Rewriteable, dual layer media

High Definition DVD (HD DVD)

 

Type:

Optical storage media

Introduced:

2006

Active:

Only by existing users

Cessation:

Format abandoned in 2008

Capacity:

Standard size disk capacity ranges from 15-60 GB (although 60 GB disk is very rare. Common large capacity is 30 GB). Mini-HD DVD capacity ranges from 4.7-18.8 GB.

Compatibility:

A HD DVD player or drive is required.

Users:

Limited. Used as data storage, particularly video, but small lifespan means it did not establish a large user base.

File Systems:

UDF, ISO9660

Common Manufacturers:

Toshiba

 

Recognition

As with standard DVDs, HD DVD come in the 12cm and 8cm size and look identical to other DVDs, save for any labelling. HD DVD was indented to be the successor to standard DVDs with its increased capacity of 30GB. However, HD DVDs were in direct competition with blu-ray disks, another high density optical disk. Blu-ray proved to be the more popular choice and the HD DVD format was abandoned by creators Toshiba in 2008.

Again, like standard DVDs, an HD DVD capacity depends on its construction and DS DL HD DVDs are also rare like similar standard DVDs.

Construction

Capacity
Single Sided and Single Layered (SS SL)

15 KB
Single Sided and Double Layered (SS DL)

30 KB
Double Sided and Single Layered (DS SL)

30 KB
Double Sided and Double Layered (DS DL) 60 KB

 

The capacities for miniDVDs are:

Construction

Capacity
Single Sided and Single Layered (SS SL)

4.7 KB
Single Sided and Double Layered (SS DL)

9.4 KB
Double Sided and Single Layered (DS SL)

9.4 KB
Double Sided and Double Layered (DS DL) 18.8 KB

 

HD DVDs are only available in two speeds. The original speed writes data to the disk at a rate of 4.5 MB/s. 2x writes data at a rate of 9 MB/s.

HD DVDs are available in the –R and –RW formats, though not DVD+. These follow the Orange Book standards and the format is often stated clearly on each disk.

An HD DVD drive or player is required in order to read an HD disk. These are backwards compatible so can also read CDs and standard DVDs. HD DVD drives can be used with computers running Windows XP, Windows Vista, Mac OS 10 (version 10.5) and many varieties of Linux.

Blu-ray Disks

Type:

Optical storage media

Introduced:

2002

Active:

Yes [2010]

Cessation:

–

Capacity:

7.5-50 GB

Compatibility:

Blu-ray disks only work in Blu-ray disk players, which at the time of writing [2010] are inbuilt on some modern computers, but these do not dominate the market.

Users:

Mainly used for high-definition video (pre-pressed films) and video games (e.g. Playstation 3). This is still a relatively new technology and has not yet had much impact on the data storage market.

File Systems:

UDF, ISO9660

Common Manufacturers:

Sony, Mitsubishi, Philips, Hitachi, Panasonic

Recognition

Blu-ray disks look identical to CDs and DVDs and like them come in 12 and 8cm sizes, both of which come in recordable (BD-R) and rewritable (BD-RE) formats.

 

All Blu-ray disks are single sided, but like DVDs can be single or double layered, which affects the disk capacity:

 

Size

Single Layer Capacity

Dual Layer Capacity
Standard Blu-ray (12cm) 25 GB 50 GB
Mini-Blu-ray (8cm) 7.8 GB 15.6 GB

-Victoria Sloyan

Media Recognition – Optical Disks part 2

20th century, 21st century, Digital archives, Modern, , , ,

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.

-Victoria Sloyan

 

 

 

 

 

Media Recognition – Optical Disks part 1

20th century, 21st century, Digital archives, Modern, , , ,

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.

-Victoria Sloyan

Carved in Silicon

21st century, Digital archives, Modern, , , , , , , ,

Just found an article on the BBC site that is of interest – ‘Rosetta stone’ offers digital lifeline. Some nice pointers to research on the life of CDs and DVDs with numbers to use at presentations and it is comforting to read that what we’re trying to do Just Aint Easy(tm).

I rather like this too:

“…the digital data archivists’ arch enemy: magnetic polarity”

(I added the bold!)

Does that make digital archivists like the X-Men ? 😉

-Peter Cliff