资料来源 : pyDict

磁带

资料来源 : WordNet®

magnetic tape
     n : memory device consisting of a long thin plastic strip coated
         with iron oxide; used to record audio or video signals or
         to store computer information; "he took along a dozen
         tapes to record the interview" [syn: {mag tape}, {tape}]

资料来源 : Free On-Line Dictionary of Computing

magnetic tape
     
         (Or "magtape", "tape" - {paper tape} is now
        obsolete) A data storage medium consisting of a magnetisable
        oxide coating on a thin plastic strip, commonly used for
        {backup} and {archiving}.
     
        Early industry-standard magnetic tape was half an inch wide
        and wound on removable reels 10.5 inches in diameter.
        Different lengths were available with 2400 feet and 4800 feet
        being common.  {DECtape} was a variation on this "{round
        tape}".
     
        In modern magnetic tape systems the reels are much smaller and
        are fixed inside a {cartridge} to protect the tape and for
        ease of handling ("{square tape}" - though it's really
        rectangular).  Cartridge formats include {QIC}, {DAT}, and
        {Exabyte}.
     
        Tape is read and written on a tape drive (or "deck") which
        winds the tape from one reel to the other causing it to move
        past a read/write head.  Early tape had seven parallel tracks
        of data along the length of the tape allowing six bit
        characters plus {parity} written across the tape.  A typical
        recording density was 556 characters per inch.  The tape had
        reflective marks near its end which signaled beginning of tape
        (BOT) and end of tape (EOT) to the hardware.
     
        Data is written to tape in {blocks} with {inter-block gaps}
        between them.  Each block is typically written in a single
        operation with the tape running continuously during the write.
        The larger the block the larger the data {buffer} required in
        order to supply or receive the data written to or read from
        the tape.  The smaller the block the more tape is wasted as
        inter-block gaps.  Several logical {records} may be combined
        into one physical block to reduce wastage ("{blocked
        records}").  Finding a certain block on the tape generally
        involved reading sequentially from the beginning, in contrast
        to {magnetic disks}.  Tape is not suitable for {random
        access}.  The exception to this is that some systems allow
        {tape marks} to be written which can be detected while winding
        the tape forward or rewinding it at high speed.  These are
        typically used to separate logical files on a tape.
     
        Most tape drives now include some kind of {data compression}.
        There are several {algorithms} which provide similar results:
        {LZ} (most), {IDRC} ({Exabyte}), {ALDC} ({IBM}, {QIC}) and
        {DLZ1} ({DLT}).
     
        See also {cut a tape}, {flap}, {Group Code Recording},
        {spool}, {macrotape}, {microtape}, {Non Return to Zero
        Inverted}, {Phase Encoded}.
     
        (1997-04-05)