A legacy magnetic tape technology from StorageTek that used half-inch, single-hub cartridges similar to IBM's 3480/3490 formats, but employed helical scan recording rather than linear (parallel tracks along the length of the tape). The Redwood SD-3 drive supported 10, 25 and 50GB cartridges (native). StorageTek's Powderhorn library held a mix of SD-3 and 3480/3490 cartridges. See magnetic tape
and helical scan
Redwood cartridges are the same overall size as IBM's 3480/3490 formats, but the door mechanism and internal recording formats are different. Redwood uses helical scan, while IBM uses linear recording.