Many NSSDC data are held on both 9-track tape (1/2 inch x 2400 ft, on 10.5"-diameter reels) and 3480 tape cartridges (1/2 inch x 541 ft, in 5" x 4" x 1" cartridges). However, fewer data arrive at or are disseminated by NSSDC on 9-track tapes than in past years, although the tapes do represent a known and relatively stable medium of capacity (150 MB) appropriate to many older data sets. The 3480 cartridge tapes are used almost exclusively for internal management and not for mailings. Older technology 7-track tapes are essentially phased out from NSSDC, although NSSDC retains 7-track read capability to support the rescue of important data NASA-wide.
Over the past few years NSSDC has accepted increasing volumes of data on 4-mm DAT and 8-mm Exabyte tape for archiving and has responded to significant numbers of requests for data on such media. These tapes are 90 m and 112 m in length and are in cassettes 75 x 54 x 10.5 mm and 95 x 62.5 x 15 mm. Because the capacities of these media are in the 1-5 GB range, NSSDC has chosen to back up incoming tapes of this type with tapes of the other size (i.e., back up 4-mm tapes with 8-mm tapes and vice versa), pending final judgment on the medium to which to move these data. NSSDC does not plan to do long-term archiving on these helical-scan tapes.
Digital Linear Tape (DLT) is the tape type to which NSSDC is moving most aggressively. These tapes are longitudinally recorded 1/2" x 1167' tapes in 4" x 4" x 1" cartridges and have capacities in the 5-10 GB range. NSSDC's mass storage environment (NSSDC Data Archive and Distribution System [NDADS]) has recently been augmented with a DLT jukebox with a 5 TB capacity. In addition, NSSDC is seriously assessing a move of its deep-archived data holdings to DLT tape as a good compromise among standards, capacity, and longevity.