Editing Tape library (section)

=== Role of tape libraries and librarians ===
[[Image:Tape Retention Scratch Control triplicate form.jpg|thumb|upright=0.7|left|Tape Retention / Scratch Control form, in triplicate]]

Mainframe computer installations often had a separate room, the tape library, to house their racks and cabinets of tapes.<ref name="popkin-pike"/> The typical workflow for running a batch job was to go into the library, pull certain tapes off the racks there and load them onto a rolling cart, move the cart into the computer area, mount the tapes onto tape drives for a production run, take the tapes off the drives when the run was over, move the cart back to the library, and put the tapes back on the library racks.  Such tape libraries existed at most computer installations.<ref name="conway-gries"/>

Even a modestly sized computer installation could have hundreds of tapes,<ref name="stern-stern">{{cite book | title=Structured COBOL Programming | first1=Nancy | last1=Stern | first2=Robert A. | last2=Stern | publisher=John Wiley & Sons | location=New York | edition=3rd | date=1980 | isbn=0-471-04913-1 | pages=494, 496, 498&ndash;499 }}</ref>
and library sizes of several thousand reels of tapes were commonplace.<ref name="conway-gries"/> 
And they could be much larger:  by the mid-1970s, the [[U.S. Census Bureau]] and [[NASA]] each had tape libraries with around one million tape reels in them.<ref name="mccracken"/>
The person in charge of all this was typically called the [[tape librarian]].<ref name="popkin-pike"/><ref name="stern-stern"/> 

In this era, there were no automated tape delivery and mounting systems, and so this action had to be done by [[computer operator]]s.<ref name="conway-gries">{{cite book |last1=Conway |first1=Richard  |last2=Gries |first2=David |year=1973 |title=An Introduction to Programming: A Structured Approach using PL/1 and PL/C |publisher=Winthrop |location=Cambridge, Massachusetts | pages=333&ndash;334 }}</ref>
These people were the ones responsible for mounting tapes onto [[tape drive]]s as part of running a job.<ref name="popkin-pike"/>
Even careful computer operators could sometimes mount the wrong tape as input to a job or present the reels of a multi-tape dataset out of order.<ref name="mccracken">{{cite book| title=A Simplified Guide to Structured COBOL Programming| publisher=John Wiley & Sons|location=New York| year=1976 | isbn=0-471-58284-0  | author-first=Daniel D. | author-last=McCracken | pages=259, 264 }}</ref> Overwriting a tape that was meant to be preserved was another potential mistake.<ref name="stern-stern"/>

It was the tape librarian's responsibility to set up procedures for the handling of tapes to minimize the chances of errors taking place.<ref name="stern-stern"/>
As one book of the era wrote, "keeping track of the whereabouts of the tapes is a formidable and responsible job."<ref name="popkin-pike">{{cite book | title=Introduction to Data Processing | author-first=Gary S. | author-last=Popkin | author2-first=Arthur H. | author2-last=Pike | publisher=Houghton Mifflin Company | location=Boston | year=1977 | isbn=0-395-20628-6 | pages=149&ndash;151, 260&ndash;263 }}</ref>