What's magtape good for anyway?

[Ed G.]

> Mag tape has
> several things that make it difficult, one is old (late 60s and through

In old movies, filmmakers often focused on spinning tape 
drives when they wanted to show a computer "thinking."  What is it 
about tape drives that made them such a powerful symbol for big, 
complicated computer systems?

> the 70s) drives had a difficult time starting and stopping without 
> breaking tape or resorting to complex(then standards) controllers.  This 
> lead to things like large interrecord gaps (start, speed up read, stop,
> backspace records, stop, read) due to the inerta of starting and stoping 
> the reels.  Also fixed record sizes were used to make blocks about the 
> same length so blocks and marks could be differentiated using simple 
> timers.

Was dectape an attempt to remedy some of these problems?  My 
hazy recollection was that you could treat dectape in some ways as if 
it were a disk.

> Magtape was for the longest time the only portable media, which lead to 
> the ansi/EBCDIC problems (Evryone else and IBM/HP).  It was generally 
> used for archival storage making file organized access excess overhead.  
> While often used as block oriented, many systems used it more as a stream 
> device where the high volume storage (relative to the disks of the time) 
> capability was available.

How much data can magtape hold?  If magtape was a portable media, 
does that mean that the manufacturers agreed on the width of 
the tape, the density of recording, the method of recording bits, 
etc.?

I have an old 9 track tape from a computer course I took in 1980.  
For sentimental reasons I'd love to get a copy of its contents.  Is 
this possible do you think?

> When processing was done on early system usually two or three drives were 
> involved as one of two were for reading  and the third was writing results
> usually due to memory size limitations of the time compared to the amount 
> of data.  Alot of magtapes lore is a result of historical use.

Is 'merge sort' an example of an application that required three tape 
drives?

 Ed

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