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How is data strored on tape.

Jacques Carriere
Regular Advisor

How is data strored on tape.

Can someone explain to me how data is stored on tape. For example, if we are talking MB/s speed, does this mean the data is stored 1 bit wide containing 1 byte upward.

eg) Data stored 1 bit wide containing 1 byte of data.
------------
-8
-7
-6 1 byte
-5
-4 tape ......>>>>>
-3
-2
--------------
3 REPLIES
A. Clay Stephenson
Acclaimed Contributor

Re: How is data strored on tape.

Your question is all but impossible to answer because it depends upon the tape technology; moreover, if compression is involved, an identical bit pattern could represent different characters depending upon the translation table used at the time.

By far, the simplest format is the 9-track open reel format (which is all but extinct these days). The data were encoded as 8 tracks (1 for each data bit) for each octet plus a parity bit.

Newer schemes are much more complicated as the tape may pass over a rotating head at an angle to produce helical tracks.



If it ain't broke, I can fix that.
Torsten.
Acclaimed Contributor

Re: How is data strored on tape.

Technology is different (e.g. DLT vs. LTO).

Starting point for you could be

http://www.lto.org/newsite/html/about.html

or

http://en.wikipedia.org/wiki/Linear_Tape-Open

or

http://en.wikipedia.org/wiki/Digital_Linear_Tape

in case of DLT.

Hope this helps!
Regards
Torsten.

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Michael Steele_2
Honored Contributor

Re: How is data strored on tape.

Its hard for me to understand your question so I've pasted in some facts that you can use for foundation. To add to what Mr. Clay is explaining about 9 track tapes, here is the backup command 'dump'. Which was made for 9 track tapes. Refer to how the "bytes per inch" and tape length change as the density of the device changes.

Approximate capacity of 60m DDS tape = 1.3G bytes
Approximate DDS tape density = (1.3G bytes) / (60 m) = (550K bytes/in)

dump assumes an inter-record gap (IRG) of 0.3 in for density = 6250,
0.7 in otherwise.

dump uses a default blocking factor of 10 for density < 6250,
32 otherwise.
================
density = 550000
blocking factor = 32 (default)
assumed IRG = 0.7 in

Block length = (32K bytes/block) / (550K bytes/in) + (0.7 in) = (0.76 in)

Effective tape length =
(1.3G bytes) / (32K bytes/block) * (0.76 in/block) = (2511 ft)


Effective tape length =
(1.3G bytes) / (32K bytes/block) * (0.76 in/block) = (2511 ft)
================
density = 6250
blocking factor = 32 (default)
assumed IRG = 0.3 in

Block length = (32K bytes/block) / (6250 bytes/in) + (0.3 in) = (5.54 in)

Effective tape length =
(1.3G bytes) / (32K bytes/block) * (5.54 in/block) = (18325 ft)
===============
density = 1600
blocking factor = 10 (default)
assumed IRG = 0.7 in

Block length = (10K bytes/block) / (1600 bytes/in) + (0.7 in) = (7.10 in)

Note: This is for old tape technology. These numbers will significantly change with newer technology.
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