Digital Media
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DIGITAL MEDIA Summary the preceding information on the medium. For On-going and rapid advances in technology require example, if you want to view a specific portion of you to store electronic records on media that a videotape, you must first fast-forward through enable you to meet long-term operational and legal the preceding portion of the videotape. requirements. Your records must be trustworthy, ◆ Random. Some digital media allow users to access complete, accessible, legally admissible in court, the stored information from any physical place and durable for as long as you need them. Because on the media. For example, when you put a disk every digital storage option will eventually become into your personal computer’s disk drive, you can obsolete, consider digital storage options that will access any single file stored on the disk without allow you to maintain records by migrating and/or having to first access all the files that precede it. converting them during their required retention period. Storage Measurement The storage capacity of digital media is measured in Digital Data Storage bytes, the basic unit of measurement: Electronic records are digital data that are stored ◆ 1,024 bytes make a kilobyte (KB) on digital media. Digital data exist, at their most ◆ 1,024 KBs make a megabyte (MB) or 1,024,000 basic level, as just zeros and ones, or on and off. bytes For example, black and white photographs in the ◆ 1,024 MBs make a gigabyte (GB) or newspaper are printed as a series of either black 1,024,000,000 bytes or white dots (0 or 1, on or off). The complex organization of a large number of dots allows the ◆ 1,024 GBs make a terabyte or 1,024,000, 000,000 human eye to complete the image. The digital data bytes in an electronic record use the same principle to For example, a one-page, text-only letter might be organize digital data into the record to make the 20 KB, a graphics file might be 200 KB, and a record readable. A bit (short for binary digit) is the fifty-page, desktop-published document with smallest unit of data in a computer. A bit has a graphics might be 2 MB. single binary value, either 0 or 1. Digital data are stored on digital media. Digital Storage Options media are divided into three main types: As part of a records management plan for electronic ◆ Magnetic. On magnetic media, the digital data are records, you will need to determine where and how encoded as microscopic magnetized needles on these records will be stored. This decision will be the surface of the medium (e.g., disk or tape). based on the likelihood of access to those resources versus the overall cost in maintaining them. Your ◆ Optical. On optical media, the digital data are options for storage include the following: encoded by creating microscopic holes in the surface of the medium (e.g., disk). Online. Properly designed storage in your computer ◆ Solid State. Containing no moving parts, solid- system may provide full access to appropriate users. state media encode digital data by applying Online access means that the record is accessible small voltages that temporarily induce a group immediately through your network (e.g., on your of transistors either on or off (e.g., flash memory network server or on your personal computer’s media, USB removable memory). hard drive). This option maintains the greatest functionality but requires more expensive network storage. Sequential Versus Random Access MORE ➔ Access to digital information on digital media is South Carolina Department of Archives & History divided into two types: Electronic Records Management Guidelines ◆ Sequential. Sequential access requires the user Digital Media March 2008, Version 2 to access specific information by accessing Page 1 Nearline. Nearline storage includes storage in a — Linear Tape-Open (LTO). Linear Tape Open system that is not a direct part of your network, but is an open standard magnetic tape system. that can be accessed through your network (e.g., Similar to DLT in capacity and speed, LTO’s an optical media jukebox). This option maintains standardized format allows interoperability a moderate amount of functionality. While the between tapes and tape drives made by storage space is cheaper than online storage, different manufacturers. nearline storage requires that the user take time to — Videotape. Videotape provides sequential manipulate both the files and media of choice to access to video footage (e.g., feature films). access the records. Of the options available for magnetic storage, Offline. Offline storage refers to storage that is not overall life expectancy is greater with DLT and accessible through your network (e.g., removable LTO tape. With proper care and handling, the life media such as magnetic tape). This option trades expectancy of DLT and LTO should be greater than functionality for stability, but maintains records in ten years. Currently magnetic tape is the preferred an electronic format. method for security backups, especially when needed for long-term retention. Magnetic Media Magnetic media include: Optical Media ◆ Magnetic disk. Magnetic disks include the hard Optical media options include: disk found inside your computer that stores the ◆ Compact Disk (CD). Compact disks come in a programs and files you work with daily. Magnetic variety of formats. These formats include CD-ROMs disks provide random access. Also included are: that are read-only, CD-Rs that you can write to — Removable disk. Removable disks include the once and are then read-only, and CD-RWs that relatively small-capacity floppy disks, as well you can write to in multiple sessions. CD-RW disks as the larger-capacity peripheral disks, such as have less life expectancy than non-rewritable the Iomega Zip disks. ones. CD is relatively stable and with proper error — External Hard Drive. External hard drives are checking suitable for data storage of five years encased in a plastic housing and connected before refreshing. via cable to a computer port. In this way, a ◆ Write-Once, Read-Many (WORM) disk. WORM disks single processor can have access to the data require a specific WORM disk drive to enable on multiple hard drives. the user to write or read the disk. WORM disks function the same as CD-R disks. ◆ Magnetic tape. Magnetic tapes come in reel- to-reel as well as cartridge format (encased ◆ Erasable optical (EO) disk. The user can write to, in a housing for ease of use). The two main read from, and erase from EO disks as often as advantages of magnetic tapes are their relatively they can magnetic disks. EO disks require special low cost and their large storage capacities (up hardware. to several gigabytes). Magnetic tapes provide ◆ Digital versatile disk (DVD). These disks are also sequential access to stored information which called digital video disks, but do not necessarily is slower than the random access of magnetic include video. DVD disks are types of optical disks. Magnetic tapes are a common choice for disks with more storage capacity than CD-ROMs. both long-term storage and the transport of large Various types of DVD are often incompatible. volumes of information. Because of the rapid improvements in DVD technology and incompatibility issues, DVD is — Digital Audio Tape (DAT). DATs are in a not an ideal storage medium for your records. cartridge format a little larger than a credit Common types of DVDs include: card. The industry standard for DAT cartridge format is a digital data storage (DDS) cartridge. — DVD-ROM. These DVDs are read-only disks that DDS cartridges provide sequential access. DAT also have enough storage capacity for a full- is prone to significant data degradation over length feature film. They are accessed using time. a special DVD drive attached to a personal — Digital Linear Tape (DLT). DLT is a high speed magnetic tape and drive system in cartridge MORE ➔ format that can hold up to 70 Gigabytes of South Carolina Department of Archives & History Electronic Records Management Guidelines data. Super DLT can hold up to 100 GB on a Digital Media single cartridge. DLT offers significant speed March 2008, Version 2 and storage advantages over DAT. Page 2 computer. Most of these drives are backward- migrate all data stored on them to a stable medium compatible with CD-ROMs and can play DVD such as magnetic tape. video disks. — DVD-RAM. DVD-RAM are rewritable disks with Digital Media Capacity exceptional storage capacity. They come in Table 1 summarizes the capacity of the basic digital one- or two-sided formats. Rewritable disks media options. You should research the specific have less life expectancy than non-rewritable medium and manufacturer for exact specifications, ones. including cost. Because of rapid technology — DVD+RW and DVD-RW. These are a direct developments in a highly competitive market, the competitor to DVD-RAM that offer similar costs for each option change frequently. functionality, are rewritable and have slightly Table 1: Storage Capacity of Digital Media Options greater storage capacity. — DVD-R and DVD+R. DVD-Rs and DVD+Rs can be Storage Media Capacity (Uncompressed) written to once and are then read-only. Magnetic Media — DVD+R DL also called DVD+R9 (DL stands for External hard disk Up to 1 TB Dual Layer). Employs two recordable dye layers, Removable disk 1.44-120 MB each capable of storing nearly the 4.7 GB capacity of a single-layer disc, almost doubling Magnetic tape 20-180 MB the total disc capacity to 8.55 GB. DAT 24+ GB — DVD+RW DL is a rewritable optical disc with DLT 70+ GB storage cpacity of 8.5 GB.