Before you determine which digital media will meet your long-term legal and operational needs, familiarize yourself with the following key concepts:
- Digital Media
- Magnetic Media
- Optical Media
- Solid State Media
- Digital Media Capacity
- Media Life Expectancy
- Care and Handling of Digital Media
- Storage Options
- Performance Issues to Consider
Digital data is stored on digital media. Digital media can be divided into three main types:
- Magnetic. On magnetic media, the digital data is encoded as microscopic magnetized needles on the surface of the medium (e.g., tape).
- Optical. On optical media, the digital data is encoded by creating microscopic holes in the surface of the medium (e.g., CD or DVD).
- Solid State. Containing no moving parts, solid state media encode digital data by applying small voltages of electricity that temporarily induced a group of transistors either on or off. (e.g., flash memory cards, USB removable media).
Based on the characteristics of the different types of media, access to the information is divided into two categories, sequential and random access.
- Sequential. Sequential access requires the user to access specific information by accessing the preceding information on the medium. For example, if you want to view a specific portion of magnetic tape, you must first fast-forward through the preceding portion of the tape.
- Random. Some digital media allow users to access the stored information from any physical place on the media. For example, when you connect a flash drive to your computer or insert a DVD, you can access any single file stored on the media without having to first access all the files that precede it.
When choosing a media one must also consider the purpose for storing the data. How long will the records need to be accessible? Who will need to access the files? Are there are legal requirements associated with ensuring the authenticity of the records? If so, Write-Once Read-Many (WORM) technology should be considered. WORM technology originally was an optical media option. It required a special WORM disk drive to enable the user to read or write to specific WORM disks. Today, WORM technology is also available to use with magnetic media, for a lower price with a higher capacity. As long as the machine can recognized WORM tapes, there is no need for a separate tape drive.
Magnetic media includes:
Magnetic Disk. Magnetic disks include the hard disk found in your computer that stores the programs and files you work with daily. Magnetic disks provide random access. Also included are:
- External Hard Drive. External hard drives are encased in housing and connected via cable to a computer port.
- Network Environment. Multiple hard drives are connected to each other in a way that shares resources and information, creating a network.
Magnetic Tape. Magnetic tapes come in reel-to-reel, as well as cartridge format (encased in housing for ease of use). The two main advantages of magnetic tapes are their relatively low cost and their large storage capacities. Magnetic tapes provide sequential access to stored information, which is slower than the random access of magnetic disks. Magnetic tapes are a common choice for long-term storage or the transport of large volumes of information. WORM technology is available with many of these tape formats. The only requirement is that the machine is capable of recognizing the special WORM tape. As an example, Linear Tape-Open (LTO) is an open-standard magnetic take system that allows interoperability between tapes and tape drives made by different manufacturers.
Optical media options include:
Compact Disk (CD). Compact disks come in a variety of formats. These formats include CD-ROMs that are read-only, CD-Rs that you can write to once and are then read-only, and CD-RWs that you can read and write to in multiple sessions. CD-RWs have less life expectancy than non-rewritable disks. CDs are relatively stable and with proper error checking suitable for data storage of five years before refreshing.
Standard Definition Digital Versatile Disk (SD-DVD/DVD). These disks are also called digital video disks, but do not necessarily include video. DVD disks have more storage capacity than CD-ROMs. DVDs come in various types +/- and may or may not be compatible with each other (see list below). When DVDs players and recorders were first developed they would only play the + or – formats, not both. Today, however, most DVD recorders and players will accept either the +/- format. The life expectancy of DVDs are similar to that of CDs but with the ever changing technology, may not be the most reliable storage medium for long-term files. Common types of DVDs include:
- DVD+R and DVD-R. DVD+R and DVD-Rs can be written to once and then are read only. (4.7 GB per layer) DVD-Rs are more commonly compatible with older machines; DVD+Rs were only officially recognized as an official DVD format in 2008.
- DVD-RAM. These DVDs are rewritable disks with exceptional storage capacity. They come in one- or two-sided formats. Rewritable disks have less life expectancy that non-rewritable ones.
- DVD+RW and DVD-RW. These are direct competitors to DVD-RAM with similar functionality, are rewritable and have slightly greater storage capacity.
Write-Once, Read-Many (WORM) disk. WORM disks require a specific WORM disk drive to enable the user to write or read the disk. WORM disks function the same as CD-R and DVD-R disks.
High-Definition DVD. Envisioned to be the successor of standard definition DVDs. High-definition DVDs have higher storage capacity than a standard definition DVD. A single sided HD-DVD can store 25 GB rather than the 4.7 of a SD-DVD. The optical technology uses a blue ray (rather than a red ray) which has a shorter wavelength which increases the storage capacity of the disks. Blu-Ray and HD-DVD were two competing formats. Support for HD-DVD was discontinued in early 2008.
- Blu–ray Disc. Developed by the Blu-Ray Disc Association, the main uses for this disk are for video, computer games and data storage. BD-R and BD-RE are the read-only and rewriteable formats of the Blu-ray disc.
- HD-DVD. Supported by Toshiba. A competitor of Blu-Ray, that also offered higher storage capacity than previous DVD formats. Support for HD –DVD +/- Rwas discontinued in early 2008, making Blu-ray the format of choice for higher capacity optical storage.
Optical cards. Optical cards, also known as “smart cards,” are the size of a credit card. They come in read-only and read-write formats. They are not in widespread use except for limited applications, such as automatic teller machines, personal identification for security systems, and airline reservations.
Optical tape. Optical tape is tape coated with optical recording material. Optical tape is not widely used.
Solid State Media
Solid state media is used in various removable devices utilizing flash memory including digital cameras, cell phones, computer games, music players, and video recorders. Small cards and “memory sticks” store images, games, music, data, programs, and video. Storage capacities of these cards or sticks are ever increasing; when they were originally introduced their size was between 32 MB and 512 MB; there are now models that can store over a terabyte.
Memory cards and flash drives (memory sticks) can be connected to a computer via card reader or USB port to assist with data transfer between devices. The small size, portability, and no moving parts make solid state media attractive. Data is accessed randomly. All formats are re-writable. Long-term storage capabilities of solid state technology are still being studied. Some examples of solid state media are listed below.
- Flash Memory Cards. Memory cards are made in a variety of sizes and range from around an inch square to around a centimeter long. Larger cards are often used in digital cameras and smaller cards in cell phones. There is a great variety of card types in use as well as the storage size of the cards.
- USB Flash Drives. Connected to a computer via a USB port, these ‘drives’ (storage devices) are a very portable option for data transfer.
- Solid State Hard Drives. Uses solid state memory to store data, with more capacity than memory cards and flash drives. The drives have no moving parts which are an advantage, but the cost per GB is currently more than with an external hard drive.