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Definition: open reel

Open reel refers to magnetic tape coiled in a reel. The drives have two spindles; one for the supply reel and another for take-up. Open reels gave way to self-threading tape cartridges, which contain both reels (see magnetic tape).

Starting in the 1950s
The first computers used open reel half-inch digital tapes with seven parallel tracks that stored a 6-bit character plus parity. Starting in the 1960s, 9-track tapes supported the 8-bit byte and parity. Also in the 1950s, consumers began using quarter-inch open reel tapes for recording analog audio. See half-inch tape, magnetic tape and byte.

Manual Threading
The supply reel is manually mounted on one spindle, and the loose end of the supply tape is threaded around a magnetic head and onto the empty take-up reel on the other spindle.

There Were Millions of Them
For more than 50 years, open reel tapes were used for data storage. For a short time after the turn of the century, half-inch open reel tape drives were still manufactured. Widely used computer standards hang around longer than one might think. (Bottom image courtesy of The Computer History Museum, www.computerhistory.org)